ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 481 



Epidermis of Petals.* — Herr G. H. Hiller has examined the struc- 

 ture of the epidermis of the petals in a large number of flowers. He 

 calls attention especially to the common occurrence of ribbing in the 

 epidermal cells, where, of two adjacent cells, the wall of one only is 

 strongly thickened in places, forming folds which project into the 

 cell-cavity of the other cell. The statement of some observers that 

 this structure does not occur with brightly coloured flowers is 

 incorrect. It is found especially with petals of delicate texture, and 

 more commonly with dicotyledons than monocotyledons. The degree 

 both of the ribbing and of the waviness of the walls may vary even in 

 different parts of the same petal. The outer surface of the epidermal 

 cells has a strong tendency to develope into papillte which may vary 

 in shape from segments of spheres to narrow cones. They occur only 

 in the upper part of the petals. The petals very often j)ossess stomata 

 on both sides, which differ in no important respect from those of the 

 leaves ; their guard-cells contain abundance of starch. The author 

 noticed in the petals of many plants cells of peculiar shape which 

 appear to be stomata arrested in their development. 



Notwithstanding statements to the contrary, intercellular spaces 

 very commonly occur between the epidermal cells of petals, more 

 especially on the under side ; they vary greatly in size and form, and 

 are always covered by the cuticle. They almost always result from 

 rib-like foldings of the side- walls. 



The main physiological purpose of the epidermis of petals, as of 

 that of leaves, is to protect against excessive transpiration; the 

 papillaa serving as a reservoir of water. The epidermal cells, both on 

 the upper and under side of petals, are very commonly filled with 

 starch, especially when young ; it appears to be partially consumed 

 by the rapid growth of the petals. 



Bursting of Ripe Fruits.f — ^Herr C. Steinbrinck, commenting on 

 the paper on this subject by Leclerc du Sablon,J objects to his con- 

 clusions in some particular instances, while in his general conclusions 

 he charges him with adopting without acknowledgment the results of 

 previous writers. Steinbrinck re-states the general law that in the 

 majority of cases the hygroscopic tensions which cause the bursting 

 of dry fruits do not depend altogether or at all on differences in the 

 capacity for swelling of different portions of tissue, but chiefly or 

 entirely on differences in the shrinking of stretched cells. The actual 

 elements are usually so arranged that — either by themselves or in 

 conjunction with differences in the capacity of swelling of their walls 

 — when they dry up, forces are called out which rupture the pericarp 

 at the point of least resistance, and bring about changes of form 

 serviceable in the dissemination of the seeds. 



Comparative Anatomy of the Cotyledons and Endosperm.§ — 

 M. J. Godfrin has made a detailed examination, in a great variety of 

 plants belonging to widely separated natural orders, of the develop- 



* Pringsheim's Jahrb. f. Wiss. Bot., xv. (1884) pp. 411-51 (2 pis.), 

 t Ber. Deutsch. Bot. Gesell., ii. (1884) pp. 397-405. 

 % See this Journal, ante, p. 276. 



§ Ann. Sci. Nat.— Bot., xlx. (1884) pp. 5-158 (6 pis.). 

 Ser. 2.— Vol. V. 2 I 



