April 1892.] THE BOTANICAL SOCIETY" OF EDINBURGH. 413 



concise account of the phenomena of reproduction, as far as 

 these are known to occur up to the present time, in both 

 vegetable and animal life, could not have been written. Yet 

 I must differ in some points, as the observations I have been 

 fortunate enough to make in my study of the embryo-sac, 

 point to a solution of the problems of sex in a different 

 direction. 



We must be very guarded in attributing special functions 

 to the different organs of a cell, and althouo-h the " nucleus " 

 of a cell seems to have " the same sort of relation to the cyto- 

 plast as a nerve-centre has to an organism," we are not as 

 yet able to say which part of the nucleus has such a function. 

 Is it the endonucleolus with its radiating fibres, the nucleolus, 

 the nuclear-chromatin or achromatin, &c. ? 



That cytoplast and nucleus react upon one another 

 mutually I admit, but cannot agree to the view that this 

 reaction ceases, due to prolonged stimulation of the nucleus 

 by its own cytoplast. The author points out himself that 

 continuous vegetative reproduction is interfered with in 

 sexually differentiated organisms ; but as in primarily non- 

 sexual organisms, and in those which have returned from a 

 sexual to a non-sexual condition (as, e.g., often occurs in the 

 Banana), we have unlimited vegetative growth, I believe all 

 the author could imply would be that in sexually differen- 

 tiated organisms the nucleus had become specially sensitive 

 to reactions of its own cytoplasm, and that for this reason 

 it was soon tired out. Then sex would be equivalent to the 

 development of a higher degree of sensibility on part of the 

 nucleus ; a sensibility which was readily blunted by the same 

 kind of stimuli arising in its own protoplasm, and which was 

 restored in the zygote by the nucleus coming in contact with 

 new cytoplasm, producing different kinds of stimuli from 

 those it has been accustomed to in its own cell. 



The author has also omitted to point out why the game- 

 togonium of Ulothrix gives rise to either many microgametes 

 or to comparatively few megagametes, and how in Pandorina, 

 in which the number of gametes is always eight, an impulse 

 is given to the development of either large or small gametes. 



To assume, further, that the megagamete prepares itself 

 for the reception of the microgamete by storing up nourish- 

 ment " to give its zygote a good start," and that the micro- 



