96 INTRODUCTION TO CYTOLOGY 



the maturing endosperm of Ricinus the protein-containing vacuole passes 

 through a reticular stage and breaks up into smaller ones which, through 

 dehydration, become aleurone grains (Fig. 49, / to j). At the time of 

 germination the process is reversed : the grains absorb water and become 

 small vacuoles, which then coalesce to form a network and finally a 

 large vacuole (Fig. 49, I to o). It has accordingly been concluded by 

 the Dangeards that the vacuome is an autonomous system present in all 

 plant cells and multiplying by repeated division. 



That vacuoles may arise de novo is maintained by Guilliermond, who 

 has made intensive studies of fungi and terminal meristems in the living 

 condition. In vitally stained young branches of Penicillium hypha? and 

 developing buds of yeast they are said to appear often without any 

 connection with the vacuome of the main portion. The same is reported 

 for Saprolegnia. Dangeard (1927c) contends that in untreated hyphse 

 and yeast the new vacuoles can be seen to originate from the old ones 

 by budding or constriction and that the vital dyes used by Guilliermond 

 cause certain alterations in the morphology of the young vacuome. No 

 evidence for origin de novo is found in Erisiphe.^ The question of the 

 origin of vacuoles in hyphse therefore remains unsettled. 



In their studies on terminal and lateral meristems of vascular plants 

 Bailey and Zirkle found no evidence for the origin of vacuoles de novo, 

 although, as Zirkle points out, such a mode of origin in a cell whose 

 vacuoles are constantly fragmenting, changing their shape, and fusing 

 would easily escape notice. 



Cell Sap. — The fluid in the ordinary vacuoles of plants is somewhat 

 viscous and usually homogeneous in appearance, and it quickly shows a 

 marked increase in viscosity when exposed to the air. It consists df 

 water with a variety of substances in molecular and colloidal solution. 

 Analyses have shown that the following elements and classes of com- 

 pounds occur in such saps: magnesium, aluminum, sodium, potassium, 

 calcium, manganese, iron, nitrogen, phosphorus, sulphur, chlorine, iodine; 

 organic acids (oxalic, malic, citric, acetic, tartaric, formic, etc.); alcohols; 

 carbohydrates (dextrose, fructose, lactose, inulin, etc.); slimes, gluco- 

 sides; anthocyanin and soluble yellow pigments, most of which exist in 

 the form of glucosides; amides (glutamin, asparagin) ; alkaloids; albumins; 

 certain enzymes; tannins; a variety of other aromatic compounds (see 

 A. Meyer, 1920). The vacuole is thus a reservoir of nutritive materials 

 and a depot for by-products. 



Although the sap rather characteristically shows an alkaline reaction 



in meristematic cells, its behavior toward vital dyes indicates a change 



to a neutral or acid state with the appearance of organic acids and certain 



phenolic compounds, such as tannin (P. Dangeard, 1923a). In the 



* Guilliermond (19256) on Penicillium and yeast, Cassaigne (1931) on Saprolegnia, 

 Baache-Wiig (1925) on Erisiphe. 



