ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 91 



the dark. Experiments on dried cotyledons confirmed Wilhelm's 

 idea that in annual plants the callus does not again disappear from 

 sieve-tubes that have ceased to be active. 



Mechanical Function of the Epidermis.* — J. E. F. af Klercker 

 describes the peculiar structure of the epidermis of the nearly leafless 

 stem of AphyllantJies monspeliensis, which is provided with a number 

 of longitudinal ridges, caused by great thickening of the walls of the 

 layer of epidermal cells which immediately surrounds the internal 

 tissue. This layer corresponds in function to the epidermal and 

 sub-epidermal collenchyma- or bast-bundles of other stems. At the 

 base of the stem the mechanical function of this epidermis is per- 

 formed by the epidermis of the leaf-sheaths. 



Comparative Anatomy of Leaves of Chrysosplenium.t — In a 

 detailed comparative anatomy of the leaves of Chrysosplenium, J. 

 Borodin mentions a peculiarity in the stomata of C. alternifoUum. 

 They are formed in groups, exclusively on the under side of the 

 leaf, and in each group the separate stomata are developed at very 

 different times. The same peculiarity was observed, though less 

 strikingly, in other species of the genus. 



Adaptation of Leaves to their environment.^ — F- Johow de- 

 scribes the various contrivances by which, in tropical countries, 

 leaves are protected from the too intense direct sunlight which would 

 otherwise destroy the chlorophyll. One very common arrangement 

 for this purpose is the vertical position of the lamina of the leaf, 

 which is either hereditary in all the leaves, or occurs only in those 

 which are exposed to the sun. The same object is effected by the 

 folding of the leaf on the mid-rib, a proceeding greatly facilitated by 

 the parallel venation of most endogens. Another contrivance for the 

 same purpose is the periodical movement of leaves or of segments of 

 leaves. The red pigment of young leaves and branches, and the hairy 

 covering of the veins of leaves, protect the conducting tissue from too 

 intense light. Protection against too rapid transpiration is afforded, 

 in some cases, by the partial or complete suppression of the lamina ; 

 in others by the very great development of the cuticle or epidermis, 

 which in some tropical plants is carried to an excessive extent ; in 

 others again by the preponderance of palisade-tissue in the hypo- 

 dermal region; while in leaves which remain in the shade, spongy 

 parenchyma with large intercellular spaces is the prevalent form of 

 tissue. 



Dehiscence of Anthers.§— M. Leclerc du Sablon describes the 

 mechanical contrivance which causes the dehiscence of anthers, pro- 

 duced by a " fibrous layer " beneath the epidermis, composed of cells 

 with peculiar thickenings, but which are otherwise very thin-walled. 

 The contraction of the anther-valves during dehiscence is always 



* Bot. Centralbl., six. (188i) pp. 215-21. 



t Albeit. St. Petersb. Naturf.-GeselL, xiv. (1883) pp. 32-40 CRussian). See 

 Bot. Centralbl., xix. (1884) p. 291. 



J Pringsheim's Jahrb. Wiss. Bot., xv. (1884) pp. 282-310. 

 § Comptes Rendus, xcix. (1884) pp. 392-5. 



