ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 113 



on the form of the leaves ; and he finds an almost inexhaustible supply of 

 beautiful adaptations to purpose in this respect ; while, on the other hand, 

 there are not wanting cases in which it would seem that the adaptation is 

 not complete. 



Leaves of Water-plants.* — M. J. Costantin publishes the results of a 

 large number of observations on the peculiarities of the morphology and 

 internal structure of the leaves of plants growing either normally or 

 accidentally in water. 



As a general law it may be stated that submersion modifies the develop- 

 ment of leaves, tending to increase their surface at the expense of their 

 thickness, whether in one plane or by numerous capillary subdivisions. If 

 a plant growing in the air is submerged the undeveloped leaves will un- 

 dergo changes in this direction, while the adult leaves will perish ; in the 

 former case the changes of medium may act directly or indirectly in bring- 

 iug about adaptations in the leaves. The capillary division of the leaves of 

 aquatic plants occurs exclusively with Dicotyledons (Banuv cuius, Myrio- 

 phyllum), while elongation in one direction is chiefly characteristic of 

 Monocotyledons (Sagittaria, ValUsneria, &c.). Many aquatic plants have 

 different forms of leaves, according as they are submerged, floating, or 

 aerial [Sagittaria, Alisma, Nuphar). 



As regards the structure of the epidermis, the immediate action of an 

 aquatic medium is manifested in the complete or approximate disappearance 

 of stomata from the submerged leaves and from the lower surface of floating 

 leaves ; and in the submerged leaves of plants normally aerial, by the dimi- 

 nution of their number on the upper as compared with the lower surface. 

 In Stratiotes the exposed portion of the leaf possesses stomata, while the 

 submerged portion of the same leaf is destitute of them. In a plant 

 growing in shallow water, the stomata may be formed even in the bud on 

 leaves which will subsequently expand on the surface or be completely 

 exposed. Further changes are shown in the walls of the epidermal cells 

 becoming rectilinear and diminishing in thickness, in the external wall 

 (cuticle) not becoming suberized, in the disappearance of hairs, and in 

 the appearance of chlorophyll in the epidermal cells. In the mesophyll 

 the lacunae show a tendency to increase in number, accompanied by a 

 reduction of the fibrovascular and other strengthening elements. The 

 palisade-tissue also disappears or becomes greatly reduced. These changes 

 appear to be the direct result of the change of medium. 



Growth of Hairs on Etiolated Organs.t — From the examination of a 

 large number of plants artificially etiolated, Herr A. Schober concludes 

 that etiolation does not itself affect the form or length of the hairs on the 

 stem, leaves, or root ; although the hairs are larger or smaller in proportion 

 to the vigour of growth of the plant itself. 



Cilia of Luzula.l — ^According to Herr F. Buchenau the cilia on the 

 leaves of all species of Luzula are expansions, not of the epidermis of 

 either surface only, but of a layer of cells resulting from the union of 

 the epidermis of both surfaces. They consist of three or four cells at the 

 base, at the apex of a single apiculate cell. In the allied genus Juncus a 

 similar structure was found only in J. trifidus. 



* Ann. Sci. Nat. (Bot.), iii. (1886) pp. 94-162 (5 pis.)- Of. this Journal, 1885, 

 p. 674. 



t Zeitschr. f. Naturwiss., iv. (1886) pp. 556-78. See Bot. Centralbl., xxviii. (1886) 

 p. 39. 



t Abhandl. Naturwiss. Ver. Bremen, ix. (1886) pp. 293-9. See Bot. Centralbl., xxvii. 

 (1886) p. 220. 



1887. I 



