Apkil 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 423 



their physiological function, and yet the trophic centre be 

 deficient in amount or quality to govern the organs. Let 

 us suppose that two unicellular organisms have the same 

 opportunity of acquiring food, but that they differ from one 

 another in this respect, that in the cell T the balance between 

 the trophic centre and its organs is in favour of the trophic 

 centre, while in the cell the reverse is the case. Then 

 the organism T will not be able to assimilate food in sufficient 

 quantity to satisfy its centre, while reversely in the organism 

 0, more nourishment will be at the disposal of the trophic 

 centre than it requires, and, by the same reasoning as above, 

 when the amount of available food was supposed to vary I 

 conclude again that in the organism T we will have great 

 activity developed, while will be characterised by its 

 passivity. 



Whatever cause may produce this loss of balance between 

 the trophic centre and its organs, it is evident that a union 

 of two cells, one deficient in the activity, and the other 

 characterised by an excessive activity of its centre, would 

 tend to restore the normal balance between the centre and 

 its organs. It is this restoration of the balance which I 

 believe to be the essential element in fertilisation. 



Conjugation of two cells is then equivalent to the new- 

 formation of one cell thus constituted that the trophic centre 

 is capable of exerting its influence over the various organs, 

 and that the organs are able to maintain their trophic centre 

 by satisfying its chemical affinities. How this loss of 

 equilibrium between the trophic centre and its organs is 

 restored in the zygote is a question which I believe my 

 observations have began to throw light upon. 



I do not believe the active male cell to effect the 

 restoration of the equilibrium, as manifested by the divi- 

 sion of the passive female cell, by acting either as a 

 ferment (v. Sachs), or by simply doubling the amount of 

 chromatin in the female cell (Strasburger, Weismann, Eyder), 

 or by being the carrier of katastates (Geddes and Thomson), 

 or by restoring the susceptibility of the female nucleus to 

 stimuli from its own cytoplasm (Hartog) ; nor have we 

 digestion of the two cells, or isophag}- as Ealph believed ; 

 but, as I have endeavoured to show, feeding of the starving 

 cell on the surplus nourishment of the over-fed cell, with no 



