From the end of the gland, when touched may be drawn out a gossamer thread of some length. The pulling out of the thread exhausts the gland in whole or in part, and causes it to collapse

Martynia.

FIGS. 35, 36, 37.-Glands of Martynia. shaped glands of which Fig. 40 shows a vertical section. In damp weather, or when not exposed to very dry air, these cups

FIG. 40.-Gland of Tecoma radicans.

FIG. 41.-Spot FIG. 42.-Stoma on fruit of same. on fruit of same.

are heaped full with a drop of glistening liquid in each. Besides these, on the surface are numerous spots, like Fig. 41, in which numerous cells are clustered into a circular form. From these we may find all gradations down to a two-celled stomate, as in Fig. 42.

On each margin of the petiole of Viburnum opulus and Passiflora are some cup-like glands which exude a sticky substance. Similar glands are found on the petioles of the cherry and some peaches.

For our present purpose enough of these hairs and glands have been described and illustrated. A large majority of plants

FIG. 43.-Glands on petiole of Snowball.

possesses something of this nature in a greater or less degree. When fresh, and especially when not exposed to direct sunlight or air which is too dry, these glands are covered with a spherical

glistening drop which is often several times the diameter of the gland.

The uses of these hairs and glands we probably now understand to some extent, but in other cases we can only guess their office. The slender-pointed hairs may serve to some extent to ward off insects. These and the scale-like hairs may prevent the delicate surface from being scorched by the sun. This is not very probable, because most of the hairs on leaves are on the under side away from the direct rays of the sun. In the case of the common mullein, the thick branching hairs probably make the plant offensive to cattle and other animals. In a similar way other plants are protected from animals.

When packed within the bud scales during winter, the young leaves and flowers of many of our trees and shrubs are well protected by these soft hairs which envelope the tender parts like a mass of cotton or wool. After expansion of the buds these hairs generally drop off.

When the hairs or spines are stout and point backward, as in Galium and Leersia, they serve well to hold up the weak plant as it rises among stouter objects.

Fruit with hooked hairs is likely to be scattered by holding fast to animals. The bloom on a cabbage leaf or plum, and the thick hairs on plants prevent them from becoming wet on the surface. The shield and star-shaped scales on Shepherdia and Deutzia, and others, may serve the same purposes as hairs. These delicate objects must protect the plant from injury on account of sudden changes of the weather. The advantage of the sting of the nettle to the plant is obviously a means of self-protection.

The function of glandular hairs in some cases is a great mystery. In the case of Martynia the writer found it caught immense numbers of small insects, and in some way seems to suck out their substance. Small insects are found to a greater or less extent caught and held fast by the glandular hairs on all or most of the plants which produce glands. In his Insectivorous Plants Mr. Darwin, by experimenting, concludes that the glands of Droseras devour animal substances. The same conclusion is reached in case of numerous other plants, as some Saxifragas, Primulas, Pelargoniums, Pinguiculas.

The glands of the trumpet creeper are active, even till the fruit is of full size and quite near maturity. They are much visited by flies, wasps, and especially by ants to such an extent that the plant is often considered a nuisance when placed near the house. The glands on the leaves of cherry trees and Viburnum are also much frequented by insects. The base of the leaves of the sunflower, locust, Pteris aquilina (a fern) and numerous other plants are freely visited by insects. Of what benefit it can be to Tecoma, Pteris, Helianthus and the cherry to be thus visited by ants is beyond my certain knowledge.

The glands of tomatoes, tobacco, petunia and many other plants secrete a substance which is offensive to most insects and other animals which might otherwise devour the plants.

Mr. Darwin has also shown that some of these plants do certainly absorb and appropriate gaseous and liquid bodies. Many ingenious experiments were made on plants of several different orders, showing that "they detect with almost unerring certainty the presence of nitrogen." Plants by their glands were fed with green-peas, raw meat, a decoction of grass leaves. These substances are acted on in exactly the same manner as by gastric juice."

Why may not these glands also draw nourishment from the particles of dust which fall on them from the air, or from the particles of soil which in many cases accumulates to such an extent as to completely cover some portions of the plant? As root hairs are active in absorbing materials from the soil including something from solid substances, why should not these active glands absorb materials from the dust and fragments of soil? The free presence of the air and light may also assist in this supposed action. This covering of the plant by the particles of soil held by

the hairs and glands may also save the plant from destruction by animals.

Of one thing the writer is certain, that these delicate objects are interesting to study. Situated as they are in immense numbers and in such great variety on the surface of so many plants, they are easily obtained and easily prepared for examination. They are excellent objects for a beginner in the use of the compound microscope; and for protracted and careful experiments, they are worthy the skill of the most accomplished scientist. In them we may spend weeks to advantage in observing the development of cells, the nucleus and nucleoli, and the gyration of the sap. In form and color they are exquisitely beautiful, while in variety they are inexhaustible.

-:0:

ON THE TRANSFORMATIONS AND HABITS OF THE

BLISTER-BEETLES.

BY CHAS. V. RILEY, A.M., PH.D.

[Continued from the April Number.]

History of Epicauta.—It is generally stated by writers on the Hive-bee that the Oil-beetle (Meloë) is one of its parasites. The possibility that our more common blister-beetles were similarly parasitic on bees, taken in connection with the frequent complaints from apiarians of the wholesale death of bees from causes little understood, led me, some years since, to pay attention to the biological characteristics of the blister-beetles, in the hope of ascertaining whether or not they really bear any connection with bee mortality. From these investigations I am satisfied that Meloë is only parasitic on the perfect Hive-bee as it is on so many other winged insects that frequent flowers; and that it cannot well, in the nature of the case, breed in the cells of any social bee whose young are fed by nurses in open cells.

I have had no difficulty in getting the eggs or the first larva of several of our vesicants, and described some of them at the Hartford (1874) meeting of the Am. Ass. Adv. Sc.; but these young larvæ refused to climb on to plants furnished to them, or to fasten to bees or other hairy insects. Nor would they nourish upon honey, bee-bread, or bee larvæ on which they were placed. They showed a proclivity for burrowing in the ground, and acted quite differently from those of Meloë or Sitaris, which not

FIG. 3-Epi

normal form.

only readily attach to bees in confinement, but which, in the case of Meloë, I have known to so crowd upon mature hive bees as to worry them to death and cause extended loss in the apiary. Explorations into the nests of Solitary bees gave no clue, and, in fact, the immense numbers in which the more common blister-beetles occur, rendered a parasitic life upon such bees highly improbable. In sweeping plants and flowers with the net, I had never met with cauta vittata: any of the first larvæ with which I had become familiar, as already indicated; while I had on several occasions, in digging ground where there was no trace of bee nests, met with the curious pseudo-pupa so characteristic of the family. While analogy and the law of unity of habit in species of the same family pointed, therefore, to a parasitic life, I began to conclude, from the facts just stated, that the parasitism was of another kind, having satisfied myself by various experiments that the triungulins did not feed on roots. Few discoveries are stumbled upon. We find as a rule that only which we anticipate or look for. In 1876, in digging up the eggs of the Rocky Mountain locust (Caloptenus spretus) at Manhattan, Kansas, the pseudo-pupæ were not unfrequently met with. The thought at once occurred to me that locust eggs might be the proper food for these blister-beetle larvæ, and it was encouraged by the fact that the Meloids abound most in those dry western regions where the Acrididæ most prevail, and by a pretty distinct recollection, which my notes support, that the years when the vesicants were most injurious to potatoes had been preceded by dry Falls, during which there had been much locust injury and, necessarily, unusual locust increase. The suspicion thus raised that these blister-beet

les preyed in the preparatory states upon locust eggs was confirmed last spring by finding the larvæ of different ages within the egg-pods and devouring the eggs of Caloptenus spretus. Mr. FIG. 4.-Macrobasis unicolor:—a normal, gray form ; b, black (murina) form; c, d, male and female antenA.N.Godfrey had, also, næ of either.

a