April 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 361 



ovules taken from a fully expanded flower be examined, and 

 only very rarely does it arise in the basal half of the cell, 

 fig. 16.* In ovules taken from immature flowers I have 

 frequently found in the earlier stages an apical and a basal 

 vacuole (fig. 14) or three vacuoles (fig. 9"^), and in the later 

 stages a great number of vacuoles of all sizes towards the 

 apex and the base of the embryo-sac-cell (fig. 13 a, 13 6). 

 Whether this bears out Went's observations,t that vacuoles 

 never appear dc novo, but that each vacuole is derived from 

 a pre-existing one, just as each nucleus and each cell is 

 derived from a previous nucleus or cell, I am unable to say, 

 but I have been unable to detect a vacuole in very young 

 sporocytes. 



What are these vacuoles ? Have they to be considered 

 as indications of degenerative processes going on in the 

 protoplasm of the cell ? Is the protoplasm becoming infirm 

 and old and no longer able to fulfil its task and to keep 

 step with the growth of the cell ? These views can hardly 

 be accepted, if we consider for one moment what an amount 

 of energy there is in the young cell and how complicated 

 the changes are it must undergo before it can give rise to 

 the mature embryo-sac. May we not consider vacuoles as 

 expansions of the channels by which fluid is normally con- 

 ducted in the cell, rather than holes arising in the protoplasm 

 because of senile changes ? Expansions developed to play 

 an important part in the physiology of the cell and to per- 

 form definite functions ? One of these functions seems to be 

 that of dilating the cell-wall to allow the protoplasm and the 

 nucleus to react on the tense walls, and to model them accord- 

 ing to requirements. But how can a vacuole perform 

 this function ? The sap within the vacuoles is rich in salts, 

 hence a tendency to diffusion of fluids of less high specific 

 gravity into the vacuole must exist, and this tendency regu- 

 lated by the protoplasm in direct contact with the vacuole 

 according to its needs, will cause a pressure to be exerted on 

 the cell-walls from within. 



The effect of the increase in size of the embryo-sac-cell 



* All the figures from fig. 16-45 are arranged in such a way that the apical 

 or micropylar part of the embryo-sac is pointing upwards, while the basal or 

 antipodal part is pointing downwards. 



t Went in Pringsheim's Jahrbiicher, vol. xxi. , 1890. 



TRANS. BOT. SOC. EDIN. VOL. XIX. 2 E 



