9S2 SUMMARY OF CURRENT RESEARCHES RELATING TO 



but vacuoles; at least this is the caso in the \ca.-vc8 o{ Mimosa pndica. 

 Many vacuoles may also contain a pigment, red in acid, blue in alkaline 

 cells, occasionally yellow. These pigments a])pear to be always con- 

 nected with the presence of tannin. 



When there are several vacuoles in a cell, tlieir contents often differ; 

 thus in many petals each cell has one large coloured vacuole and several 

 small Colourless "adventitious vacuoles"; the former contains tannin, 

 while the others do not. This selection of ditierent substances contained 

 in the cell-sai) is not due to the granular i)rotophism, which is always in 

 movement, but to the tonoplast. The i)henomcnon is not dissimilar to that 

 dis])layed by chromatopliores ; the coloured vacuoles may be comjjared 

 to chromoplasts, the uueoloured adventitious vacuoles to leucoplasts. 



The vacuoles always increase in number by division. The jirocess 

 may be observed in living cells, by allowing the preparations to remain 

 for a time in a 3-5 per cent, solution of sugar. The best materials to 

 employ are the hypha) of fuugi, pollen-grains, and epidermal hairs. In 

 the endosperm a large vacuole divides into a certain number of smaller 

 ones, which become the aleurone-grains ; on germination, the albumin dis- 

 solves, and the small vacuoles fuse again into a large one. The pheno- 

 menon of aggregation in the tentacles of Droscra is due to the largo 

 vacuoles dividing, as they do under the influence of any excitation, into 

 a large number of small vacuoles, while the volume of the cell-sap 

 diminishes. When the excitation has ceased, the vacuoles fuse again 

 into one large central vacuole. 



The principal function of the vacuoles is to incite, by their osmotic 

 force, the turgidity of the cells, thus contributing to the growth of the 

 plant. Another imi)ortant function consists in storing up substances of 

 all kinds, whether reserve-materials, such as cane-sugar, glucose, and 

 inulin, or tannin, which occurs nowhere else but in the vacuoles, and 

 which appears to serve as a protection against the attacks of animals. It 

 is probable that in the vacuoles are also localized the greater part of 

 vegetable poisons, such as the alkaloids, and that the tonoplast prevents 

 these exercising an injurious influence on the protoplasm. Another 

 class of substances stored up in vacuoles is the pigments, which are 

 chiefly connected with the visits of insects. Finally they contain 

 substances the use of which is at present unknown, such as calcium 

 oxalate. In some cases the function of the vacuoles is still obscure, as 

 in that of the aggregation of protoplasm in insectivorous plants, where 

 they may contribute to the secretion of a ferment, or to the absorption 

 of nutriment. 



Albumen in the Cell-wall.* — Herr J. Wiesner replies further to 

 Fischer's arguments "f against the validity of his demonstration of tho 

 presence of albumen in the walls of living cells. He points out that 

 Fischer must be in error in suggesting that the substance supposed by 

 Wiesner to be albumen is in reality tyrosin, since the possibility of tho 

 presence of tyrosin is excluded by the process employed. 



C2) Other Cell-contents (including- Secretions). 



Development of Aleurone-grains in the Lupin.f — Mr. A. B. Eendlc 

 describes the formation of aleurone-grains in Lupinus digitatus. Until 



♦ Ber. Dcutsch. Bot. Gcsell., vi. (1888) pp. 187-95. 



t See thitj Journal, ante, p. 602. J Aim. of Bot., ii. (1888) pp. 161-6 (1 pi). 



