brain; and it is manifestly impossible, as has been remarked by Hermann, "to localize this relationship between sensational effect and variation in amount of stimulus, which has been called the psycho-physical law of Fechner." Between the sensational effect and the first contact of the stimulus there are a series of complicated processes occurring in retina, nerve, and brain, processes undergoing incessant modification by the interchanges between these tissues and the warm circulating blood. In which of these does this relation between stimulus and conscious state occur--in retina, in optic nerve, or in brain? The only method of answering this question, so far as I know, is to examine the effects of stimulation upon these parts separately. It is manifestly next to impossible to do this in the case of the optic nerve and the brain; but by the method pursued by Holmgren in Sweden, and by Professor Dewar and myself in this country, it can be done, so far as the retina is concerned. In carrying out this method, Professor Dewar and I found that light produced a change in the electrical condition of the retina in an eye removed from the head or kept in normal conditions, and we ascertained that the general phenomena of this change corresponded with our sensational experiences of luminous impressions. We were therefore entitled to assume that the change in the electrical conditions of the retina, produced by the action of light, might be regarded as a phenomenon intimately related to those changes in the brain which result in consciousness of a luminous impression. Consequently we had an opportunity of ascertaining whether or not Fechner's law agreed with the effects of a stimulus of light in altering the electrical condition of the retina, and we found that it did so. The inference, therefore, is that the relation between degree or variation in stimulus and the corresponding sensation of a luminous impression is a function of the sense-organ or retina. MODE OF INVESTIGATING THE SENSORY ORGAN ITSELF. I may here remark that this mode of inquiring into sensory impressions has by no means been exhausted. The subjective method of observing sensational effect under the stimulus of light from revolving disks, by the contrasting of colours, by comparison of auditory sensations produced by tones of different intensity, pitch, and quality, is always open to the charge that the results may not be due to specific histological structure of the sense-organ, as is almost invariably assumed, but to the structure of the recipient of impressions from the sense-organ, namely the brain. The only way of proving that the effects are due to structural peculiarities of the sense-organ is to examine the effects of stimuli applied to the sense-organ separated from the brain by some method the same as or analogous to ours. If in these circumstances the sense-organ gives results similar to those observed in the phenomena of consciousness, then we may assume that these results are due to specific peculiarities of the sense-organ, and not to the brain. If, on the other hand, the results do not agree, then we must look in the brain for the mechanism by which these different results are produced. Thus I have always held that, as there is little or no histological evidence of complexity of structure in the retina capable of accounting for the theory of Thomas Young regarding the perception of colours, or of the facts of colour-blindness, or of the sensibility of different zones of the retina to lights of different colours, we may have to look to the complex structure of the corpora quadrigemina, cerebellum, or some portion of the cerebral hemispheres for an explanation of these facts. It may be objected that such scepticism simply removes the difficulty a little further back; but I think it better to search for facts than to be content with an hypothesis. CONCLUSION. Time will not permit me to discuss other researches in this field of inquiry, nor the interesting speculations which have sprung from them, but I think I have said enough to show the line of advance in this direction. True it is that apparently the physiological causation of many mental phenomena may be, in its precise nature, inaccessible to direct proof; but it is our duty as physiologists to push legitimate research as far as it will go. I would remark also 1876. 14 that such researches are not incompatible with those spiritual ideas, matters of faith and not of science, which are the basis of our most cherished hopes. They demand, however, caution in the scrutiny of facts, and judgment in drawing conclusions from them. More than in any other kind of scientific labour, perhaps, it is of the utmost importance here to keep the mind unbiassed-a task by no means easy. To maintain a calm unprejudiced attitude to inquiries which seem to demand a change of opinion regarding what was supposed to be final, requires an effort which varies in different persons. Some find it comparatively easy to do so, while others succeed only after a severe struggle. Still it is the state of mind which a man true to science ought to aspire to, so that while he will not be blown about by every wind of doctrine, he may be ready to accept what is apparently true when he has had it clearly put before him. In conclusion, let me observe that it would save not a little heart-burning, and might possibly remove acrimony from various scientific and social controversies, could we only remember that it is not very probable that we, in this nineteenth century, have arrived at the final solution of many problems which have puzzled wise men from the earliest times. Probably we have got nearer the truth; but it is presumptuous to suppose that we have reached the ultimate truth. Many hypotheses much in favour at present may turn out to be inadequate. Still if they serve as stepping-stones to something better, and to more rational conceptions of the mysterious phenomena about us, they will have done good service. In the mean time it is our duty vigorously to prosecute research in all departments, pushing ahead fearlessly and with that enthusiasm which is the prime mover in all great deeds, so that we may be able to transmit our department of knowledge to posterity not only less burdened with error, but with many additions of truth. BOTANY AND ZOOLOGY. [For Professor Newton's Address, see page 119.] Notes on the Pandaneœ of the Mascarene and Seychelles Islands. The genus Pandanus (screw-pine) was shown to have a general distribution throughout the tropics of the Old World, and to reach its western limit on the east coast of Africa. It is very abundantly represented in the islands of the Indian Ocean, and more especially in the Mascarene and Seychelles Islands. Altogether 19 species are definitely known from these islands; and it is possible that more may exist. Of these species Mauritius includes 11, which are all endemic; Réunion has 3 peculiar species, and perhaps a fourth one may be recog nized; in Rodriguez only two species, both endemic, are found; whilst the Seychelles group possesses three such species. In addition to those which are endemic, a Madagascar species, P. utilis, is generally cultivated for the sake of its leaves, and P. odoratissimus, of Eastern origin, is also found. The difficulties in the way of the diagnosis of species were pointed out from the scantiness and imperfection of the material as yet sent to this country. The leaves afford very little character, and it is from the fruit that specific distinctions are mainly obtained. Hitherto the stigmas have afforded the chief characters; but the author showed that many important diagnostic marks might be obtained from the endocarp and its relations to the mesocarp. On the Evolution of Sex in the Vegetable Kingdom. By G. S. BoULGER. This paper was an attempt to illustrate Mr. Herbert Spencer's law of increasing heterogeneity by the various sexual processes in the vegetable kingdom. Mention having been made of the probably asexual Protophyta, Thwaites' identification of conjugation with reproduction proper, made in 1848, was mentioned, and a summary given of the sexual classification of the Thallophytes proposed by Sachs (Lehrbuch, 4th edition) and adopted by Professor Dyer (Quart. Journ. Micr. Sci.), in which they are grouped as Protophyta, Zygosporee, Oosporeæ, and Carpospores. The types Pandorina, Mesocarpus, Spirogyra, and Podosphæra were taken as indicating sexual transition between these groups; and Sachs' description of the essential nature and elements of sexual reproduction quoted. The difference between the sexes as manifested previous to the formation of the elemental 'sperm' and 'germ' cells was then traced in the various groups, being greater and manifested earlier in the more highly organized groups. Edogonium, Vaucheria, Phycomyces, Coleochate, and Nemalion were alluded to in this connexion, and following the pedigree sketched by Sachs (Lehrbuch, 3rd edition) the 'secondary sexual organs were traced through the Floride to the ancestral Cormophyte and to the 'heterosporous Pteridophyta,' near to which he places the Cycades, the lowest type of Phanerogam. The homology between the sexual organs of Phanerogams and Cryptogams was pointed out, and Hildebrand's classification of the sexual arrangements explained. In this connexion the terms apertiflorous' (open-flowered) in opposition to 'cleistogenous,' 'approximate,' and distant,' with anthers near to or remote from the stigma, and 'homostylia,' were proposed by the author for adoption. It was then attempted to base the phylogenetic arrangement of sexual forms (the chief subject of the paper) on the law of economy of nutrition, the advantageousness of cross-fertilization producing diœcism and various intermediate stages from an original hermaphroditism. Diœcism was first traced through monccism and monoecious polygamy, Fragaria, Rumer, and a reverting sport of Begonia frigida being quoted. The diocism of the English holly has probably been reached from dioecious polygamy, as in the American forms, through an intermediate monœcism; and the monoeciously or triaciously polygamous genus Catasetum points to the origin of the latter form from the former probably through an intermediate dicecious polygamy. Dioecism may possibly arise also from dimorphism, which may be monoecious, as in Dianthus caryophyllus and D. plumarius, or dioecious, as in some Primulas. Dimorphism probably originates in 'biseriate' stamens, trimorphism in 'triseriate; but the dioecious dimorphism of Lythrum thyrsifolia would seem to arise from tricecious trimorphism by suppression. Among the Composite the transitions are easy from the equal polygamy' of Linnæus, through 'superfluous polygamy,' to 'frustraneous' on the one hand and 'necessary' on the other, from either of which monccism and diccism may arise, as in Carduus arvensis, Petasites, and Antennaria. The variety, increasing complexity, and homology of the sexual arrangements, the abundant links, and the abhorrence of the sexual union of nearly related cells are the theme of the whole paper. Two Monstrosities of Matricaria inodora. By Professor ALEXANDER DICKSON, M.D. 1st. Where the florets of the capitulum were replaced by stalked secondary capitula, some of which were in turn again similarly compound. That the secondary capitula really resulted from transformed florets was interestingly shown by the presence on the stalk of many of the outer secondary capitula of a ligulate corolla with its base embracing the axis. 2nd. Where many of the florets of the ray presented a narrow ligulate lip directed inwards, these internal lips conniving more or less over the central disk. At first sight this anomaly seemed to simulate the condition in Composite Labiatiflora ; but so far as Dr. Dickson's examinations as yet went, it would appear that the smaller lip was placed laterally to the normal line of non-union of the ligulate corolla, and therefore was not a mesial structure compressed to the inner lip of the floret in Labiatiflora. Laticiferous Canals in Fruit of Limnocharis Plumieri. Dr. Dickson showed that unusually large laticiferous canals could easily be demonstrated shining through the epidermis of the flat surfaces by which the numerous carpels are in opposition to each other. On the Occurrence in Ireland of Nuphar intermedium, Ledeb. While staying with some friends at Crombyn, in West Meath, I noticed on the borders of a small shallow lake, on peaty ground, some water-lily leaves which at once drew attention from the small size of their leaves and especially with their basal lobes standing apart or widely apart. My friend Mr. Preston Battersby, of the Royal Artillery, most kindly instituted a close search, and succeeded at last in finding one blossom, from which, together with the leaves, I have been enabled to identify the plant as Nuphar intermedium, Ledeb., var. B. Speunerianum, of Hartman's 10th edition of the 'Handbok i Skandinaviens Flora' (Stockholm, 1870), vol. i. p. 86. Our plant is also, I presume, identical with Dr. Syme's so-called variety "B. minor" of Nuphar luteum; but the stigma of the single flower gathered has 15 rays. Still the characters of the leaf bring it rather nearer to var. Speunerianum than the typical form of Ledebour's N. intermedium. A. G. MORE, F.L.S., exhibited Zostera nana from Carnarvonshire. Professor W. R. M'NAB, M.D., exhibited Choreocholax polysiphoniæ, Reinsch. Notes on the Structure of the Leaf in different Species of Abies. On Circinnate Vernation of Sphenopteris affinis from the earliest stage to completion, and on the discovery of Staphylopteris, a Genus new to British Rocks. By C. W. PEACH, A.L.S. The author stated that he had found Sphenopteris affinis in black shale at West Calder, near Edinburgh, in circinnate vernation from its earliest state to the completion of the plant, and thus had an opportunity of seeing this beautiful fern in all its various stages of growth, showing the many variations it assumes and from which, when so found, no doubt several species have been made. It is rather plentiful at West Calder, Slateford, Burdie House, Burnt Island, and other places around Edinburgh; he, however, had not found it in circinnate vernation in any other locality than the first mentioned. He next exhibited and described specimens of Staphylopteris, also from West Calder, and said the plant was a new genus to British rocks; that he had met with it first sparingly in 1874, and in the present year in some abundance there, especially in one slab. It is something like Staphylopteris Wortheni of Leo Lesquereux, figured in vol. iv. of the Geological Survey of Illinois, from "the shale of the subconglomerate coal of Arkansas:" it, however, differed from that species, first, in not showing like a star around a central point; in having no sporanges: and the flower-like parts instead of only "apparently resting on," are actually attached in pairs, hanging in a drooping manner, to small branches. As well as the one mentioned, he strongly suspected that he has another species from the same locality. Several species have been found in the rocks of Arkansas; all, however, differ from the British one. The author expressed his obligations to Mr. R. Etheridge, jun., for first calling his attention to the American work; and to Prof. Balfour for his kind notice in the 'Transactions of the Botanical Society of Edinburgh,' vol. xii. part i. page 176, both proposing that it should "bear the name of the finder." He thought it right to state that wherever he found Staphylopteris, the Sphenopteris affinis more or less accompanied it; however, the latter was most often found without Staphylopteris. As well as at West Calder, Staphylopteris has been found at Slateford by the Officers of the Geological Survey and by Mr. D. J. Brown at Straition, all near Edinburgh, and all in the Calciferous Sandstone series. A large series of Sphenopteris and Staphylopteris were exhibited by the author with drawings for illustration. On some of the Physiological and Morphological Features seen in the Plants of the Coal-Measures. By Professor W. C. WILLIAMSON, F.R.S. Proceeding from the starting point of the facts recorded in the communication made to the Geological Section, the author brought before the Biological Section some morphological facts. He showed that even in young twigs of Lepidodendron the bark consisted of three very distinct layers, viz:-an inner parenchyma, a middle prosenchyma of considerable proportionate thickness, and an outer parenchyma of which the leaves were expansions. The innermost portion, the inner parenchyma, certainly represents a plane of genetic activity, along which the multiplying cells add new layers of vessels to the exterior of the vascular cylinder on its inner surface, as it apparently increases as the number of parenchymatous cells in the opposite directions. Externally to this parenchyma is the prosenchy matous layer, into which the inner parenchyma passes somewhat gradually, but which outwardly becomes a modified mass of prosenchymatous fibre, composed of very long and narrow prismatic cells. At the first glance this layer looks like a phellem or corky layer, but its origin is a different one. Its genetic plane is at its outer surface, instead of occupying the position of the phellogen of living barks. The cells at this point become elongated radially into long fusiform ones, which soon become subdivided by a regular series of vertical cell-walls, all of which are parallel to each other and to the external surface of the stem. Subsequently each one of these parallel cells becomes irregularly subdivided into a cluster of cells, the partitions of which are vertical to the primary series. In this manner, apparently, additions are made on the inner side to the prosenchymatous layer, and on the outer one to the subepidermal parenchyma. It thus becomes evident that the bark of each of the Lepidodendroid stems possesses two parallel planes of genetic activity. It is obvious that Calamites certainly possesses the innermost of these genetic planes; and as the author's arborescent specimen exhibits no indication that the second or prosenchymatous layer has been increased from within, it becomes more than probable that when yet more perfect specimens are discovered the second or outer genetic plane will be found to be identical in all respects with what is seen in the Lepidodendra. The author concluded by calling attention to the fact that amongst a large number of the coal plants their most specialized and characteristic type features were best seen in their young state, the advance from youth to maturity being one from specialized to generalized forms, the result of which was, that the author found it almost impossible to identify detached fragments of wood or bark, and hence he regarded all attempts to establish genera and species upon such fragments as absurd. On Gigantic Land-Tortoises and a Freshwater Species from the Maltese Caverns, with observations on their Fossil Fauna. By A. LEITH ADAMS, F.R.S., Professor of Zoology, Royal College of Science, Dublin. The author exhibited and made a few observations on bones of gigantic tortoises collected by Admiral Spratt and himself in the Maltese Caverns. During the five years he was engaged in exploring the rock-cavities of Malta, * Suprà, p. 98. |