ERG AST IC SUBSTANCES 



95 



looked upon vacuoles as permanent constituents of protoplasm. This 

 theory had the support of various other workers,^ but the general tend- 

 ency for many years was to view it with skepticism. 



A new period in the study of vacuoles began with the more recent 

 researches of P. A. and P. Dangeard,^ who again advanced a theory that 



Fig. 49. — Behavior of vacuole system in certain plant cells, a-d, successive stages 

 in bud of Abies, e, pollen grain of Cephalotaxus. f-j, formation of aleurone grains from 

 vacuome in endosperm of Ricinus. k, deeply lying endosperm cell of Ricinus, with typical 

 aleurone grains, l—o, peripheral cells of Ricinus endosperm, showing development of 

 vacuole from simple aleurone grains during germination. {After P. Dangeard, 1923a.) 



the vacuome is a permanent system arising not de novo but from small 

 units in the cytoplasm. According to these observers, the vacuome 

 exists at iSrst in the form of minute "metachromes"; these absorb 

 water, enlarge, develop into a system of canals,^ and finally become one 

 or more large vacuoles (Fig. 49, a to d). It was reported further that in 



2 E.g., Van Tieghem (1888) and Went (1888). 



= P. A. Dangeard (1916 et seq.), P. Dangeard (1922, 1923, 1927c). 



* Such a system of canals had been seen several years earlier in root tips by Bensley 

 (1910), who, like Dangeard, found that they were not well preserved by ordinary 

 methods of fixation (see p. 79). 



