June 1891.] BOTANICAL SOCIETY OF EDINBURGH. 137 



gelatinous change being probably to allow of a ready passage 

 of nutritive material into the rapidly developing embryo-sac. 

 Ward explains the diffluent nature of the partitions occur- 

 ring in the embryo-sac-mother-cell as also partly due to the 

 producing cells, when they approach their limit of division, 

 losing their power to form cellulose-envelopes, a process 

 most accentuated in the formation of the tetrahedral groups 

 of nuclei, when no trace of an envelope appears. This view 

 leads to the following hypothesis : — " It will be remembered 

 that the first divisions across the embryo-sac-mother-cell 

 follow one another in such a way that the two ' cap- cells ' 

 were spoken of as being cut off from the mother-cell by 

 diffluent swollen walls ; and that, the lower cell having 

 enlarged, destroying the cap-cells, its protoplasm passes to 

 each end, and a vacuole-like clear space forms between. This 

 last division may probably be looked upon as merely a third 

 division across the embryo-sac-mother-cell, and not as the 

 tirst division of the contents of the macrospore (embryo-sac). 

 In other words, we have here a division-wall still weaker 

 than the two preceding, and the ' vacuole ' is its expression. 

 If this be so, it is possible that the embryo-sac-mother-cell 

 is really the mother-cell of four spores, two of which 

 (the cap-cells) yield up their contents to their more 

 vigorous neighbours, — to the other two, wdiich never com- 

 pletely separate, but form an ' embryo-sac ' and its contained 

 apparatus. This suggestion does not exclude the view that 

 the eight nuclei derived from that of the embryo-sac-mother- 

 cell are cells of rudimentary prothalli, but explains them as 

 belonging to two prothallial structures instead of one ; the 

 one produces a rudimentary archegonium (the egg-cell with 

 its synergidffi may perhaps be an oosphere and two neck 

 canal cells) and one vegetative cell ; the lower spore produces 

 four vegetative cells." 



In support of the view that the vacuole is a very diffluent 

 cell-wall, the occasional appearance of a septum in the 

 embryo-sac of Lobelia syphilitica is mentioned. 



To the explanations given by Ward I cannot agree, for 

 the following reasons : — 



If the ovule is a macrosporangium, and its aim the forma- 

 tion of one or of several macrospores, we must suppose that 

 it will be subject, for the attainment of this end, to the 



