ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 61 



Kespiration is carried on by the buds during winter to a slight extent, 

 both in darkness and in light. 



Absorption of Nitrogen by Plants. * — Th. Schloesing fils finds, 

 as the result of experiments, that the nitrification of ammonium salts 

 is not, for all plants, a necessary preliminary to the absorption of nitro- 

 gen into the plant. While for some plants (e.g. buckwheat) the pre- 

 ferable form of the nitrogenous food-material is that of nitrates ; others 

 (e.g. Tropseoluni) thrive better when the nitrogen is presented to them 

 in the ammoniacal form. 



C3) Irritability. 



Perception of Geotropic Irritation. — In support of his view as to 

 the nature of the conduction of geotropic irritation in plants, Dr. B. 

 Nernee f points out the importance of the existence, in certain cells of 

 the organs in question, of minute bodies having either a higher or a 

 lower specific gravity than protoplasm, and which are therefore con- 

 stantly shifting their location in the cell with changes in its position. 

 Among such particles which are of a higher specific gravity than proto- 

 plasm are leucoplasts, chloroplasts, and starch-grains ; the nucleus be- 

 haves sometimes in one way, sometimes in the other. In the root these 

 cells occur in the root-cap, and especially in the so-called columel, and 

 may be regarded as forming, by their association, a special organ. In 

 the leaves and stem, these shifting particles are found chiefly in the 

 starch-sheath, occasionally in the fundamental parenchynie. The author 

 finds such cells universally in those organs which are capable of a geo- 

 tropic irritation ; and their appearance corresponds to the period when 

 the organ becomes sensitive to geotropism. The conclusion seems in- 

 evitable that these particles, heavier or lighter than protoplasm, are 

 closely connected with geotropic sensitiveness. 



G. Haberlandt J arrives at the same conclusion, that the starch- 

 sheath, with its large and motile starch-grains, is the perceptive organ 

 for geotropic irritation. Such a typical starch-sheath occurs in the 

 nodes of Gramineae, Kubiaceaa, Caryophylleae, Polygonaceaa, &c, which 

 are all capable of geotropic curvatures. The writer gives an account 

 of experiments which seem to show that the pith retains its power of 

 geotropic curvature when tho epiderm, the collenchyme, and the greater 

 part of the cortical parenchynie have been removed ; but loses it if 

 deprived of the remainder of the parenchynie and of the starch-sheath. 



(4.) Chemical Changes (including Respiration 

 and Fermentation). 



Influence of Temperature on the Decomposition of Albumen.§ — 

 Pursuing his] investigations on the formation and decomposition of 

 albuminoids in plants, D. Prianischnikow has determined that the de- 

 composition of albumen and the formation of asparagin go on more 

 energetically at a temperature of 35° C, than at one of 28°. 



* Comptes Rendus, exxxi. (1900) pp. 716-9. 



t Eer. Deutsch. Bot. Ges., xviii. (1900) pp. 241-9. Cf. this Journal, 1900, p. 487. 



X Tom. cit., pp. 261-72 (1 fig.). 



§ Tom. cit.. pp. 285-91. Cf. this Journal, 1899, p. 509. 



