ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 981 



formed not by filaments or granules, but by a delicate layer of freely 

 projecting homogeneous green substance ; sections of uncoloured layers 

 are often observed to have round clear homogeneous drop-like bodies 

 along their periphery. An account is given of the chemical and physical 

 characters of the green-coloured portions of the unaltered cuticle, from 

 which it seems to follow certainly that the green colour is identical with 

 chlorophyll. 



The formation and growth of starch-granules in chlorophyll-granules, 

 nucleus, and protoplasm, are next discussed. In all cases starch is 

 formed by the plexuses, or by these and the ground-substance in which 

 the plexuses are imbedded. The plexuses appear in the form of rounded 

 granules ; the quantity of starch formed generally increases rapidly, so 

 that the filamentar structure of even the small granules becomes obscured. 

 The growth of the granules is due to apposition, and to either the forma- 

 tion of starch-containing processes or to that of a shell-like covering. 

 Starch-granules which are inclosed by a special thick protoplasmic capsule 

 grow at the expense of the latter. The formation of chlorophyll from 

 starch-grains is treated of at some length. 



Increase of normal Vacuoles by Division.* — Pursuing his re- 

 searches on the structure and formation of vacuoles, M. F. A. T. C. Went 

 restates his previous conclusions, viz. : — That all living vegetable cells, 

 with the possible exception of antherozoids, Cyanophycese, and bacteria, 

 inclose vacuoles, each of which is surrounded by a membrane of its 

 own, the tonoplast.^ In all young cells a division and a fusion of vacuoles 

 may be observed. All the normal vacuoles in a plant result from the 

 successive division of that of the oosphere. The tonoplasts are as much 

 entitled to be regarded as organs of the protoplasm as the nuclei or 

 the chromatophores. The protoplasm is always in movement from the 

 youngest state of the cell. Normal vacuoles are never formed at the 

 expense of the protoplasm, but only pathological vacuoles in the case 

 of the disorganization of the tissues. 



In certain cases the necessity for the tonoplast is evident, as when 

 the cell-sap contained in the vacuoles is sufficiently acid to kill the 

 protoplasm, as in BJieum and Begonia. The tonoplast offers much 

 greater resistance to reagents than the rest of the protoplasm. Thus, a 

 10 per cent, solution of nitre, sufficient to plasmolyse the cell-contents, 

 kills the protoplasm, while the vacuoles remain alive in the form of 

 colourless vesicles. The contents of the vacuoles are an aqueous 

 solution of various substances, some of them crystallizable ; the reaction 

 is usually feebly acid, sometimes, as in aleurone-grains, alkaline. At 

 first these substances are chiefly' organic and inorganic salts, afterwards 

 glucose, tannin, and albumin. Calcium oxalate occurs in the crystalline 

 state in the cell-sap, but never in the cytoplasm. Albumin may occur 

 in the soluble state, as in the case of albumin tannate or alkaline albu- 

 minates, but it may also exist in the crystalline state, as in the crystal- 

 loids of Bicinus and other plants. When these crystalloids are formed 

 in the endosperm in a state of repose, and surrounded by their tonoplast, 

 they are known as aleurone-grains. On germination, the albumin dis- 

 solves and the vacuoles again become clear. Tannin is found only in 

 the cell-sap, and the so-called vesicles of tannin are probably nothing 



* Pringsheim's Jahrb. f. Wiss. Bot., xix. (1888) pp. 295-356 (3 pis.). Of. this 

 Journal, ante, p. 243. f Sec this Journal, 1886, p. 687. 



