276 STRASBURGER : FERTILISATION IN PHANEROGAMS. 



these individual peculiarities, and subscribes to the view that the 

 changes organisms exhibit are due to inner causes rather than external 

 influences. It is allowed, however, even on this view, that the long- 

 continued action of external stimuH has some effect, ultimately 

 evoking reactions in the nuclei, which in their turn induce changes 

 in the development of the individual. 



Several other matters, all more or less pertinent to his theory of 

 generation, are dealt with by Strasburger, and that, we need hardly 

 say, with rare insight and fulness of knowledge. Among these is the 

 interpretation of the fact that when an organism is brought to the 

 close of its development it again reverts to its original condition, and 

 produces germ cells. Nageli seems to be of opinion that idioplasma 

 naturally runs through a cycle of changes which bring it back to the 

 starting point of development, and Strasburger thinks such a retrograde 

 development is shown by what occurs in those cells anxi cell-nuclei of 

 plants which build up the sexual products. Hence he regards the 

 expulsion of a part of their substance by the nuclei and cytoplasma 

 of generative cells as a part of the preparatory process by which these 

 structures are brought back to their primitive condition. The division 

 of the generative cell-nucleus is another part of this j^rocess, the result 

 being the reduction in mass of the nucleo-idioplasma it contains. By 

 this reduction the generative cell-nucleus is believed to be relatively 

 poor in nucleo-idioplasma, a circumstance that is indicated by its high 

 capacity for staining. When ready for the act of copulation, the 

 egg-nucleus and the sperm-nucleus possess an equal quantity of idio- 

 plasma, as is demanded by the phenomena of inheritance. It does 

 not follow from this, however, that they should contain equal quantities 

 of food plasma, nor that they should be equal in size. Still, as a rule, 

 the copulating cells are quite equal, though their contents may differ 

 slightly in appearance. 



In accordance with his views of the relative functions of the 

 nucleus and cytoplasma of a cell, Strasburger believes that the 

 insignificant changes which the nucleo-idioplasma experiences from 

 inner causes, or from the influence of the cyto-idioplasma, are 

 equilibrated in fertilisation through the union of cell-nuclei from two 

 different individuals. In this, indeed, he sees the advantage of 

 fertihsation, for thereby the constancy of specific characters is con- 

 tinued, and injurious modifications are not allowed to fix themselves 

 and accumulate by integration. In plants destitute of a cell-nucleus, 

 sexual reproduction is, so far as we at present kno«v, altogether 

 absent, and seeing that in the absence of fertilisation variabihty 

 usually becomes very great, this may be the cause of the difficulty of 

 limiting the species in the Protophyta. 



Naturalist, 



