204 STRASBURGER I FERTILISATION OF PHANEROGAMS. 



supply all the evidence that is necessary for the complete establish- 

 ment of the following propositions: — 



1. — The process of fertilisation consists of the copulation of the 



sperm-nucleus (brought into the egg) with the egg-nucleus. 



2. - — -Cytoplasma does not take part in the process of fertilisation. 



3. — The sperm-nucleus and the egg-nucleus are true cell-nuclei. 

 The third proposition he considers is proved by his own researches. 



For whilst elsewhere the cell-nucleus appointed for the act of fertiUsa- 

 tion, in its transformation into spermatozoids, or the cell-nucleus of 

 the same, undergoes such changes as to raise legitimate doubt as to 

 its true nature ; in the plants here dealt with, a cell-nucleus of the 

 pollen-tube comes to the egg in a quite unchanged form, and com- 

 pletes the act of fertilisation. Direct observation makes this a com- 

 plete certainty. So, the egg-nucleus of phanerogams arises from the 

 division of a mother nucleus, and in Angiosperms retains unchanged, 

 up to the moment of fertilisation, both the structure and the reactions 

 of an ordinary cell-nucleus. 



As to whether or not cytoplasma takes part in the fertiHsing 

 process, some differences of opinion still exist, and hence Strasburger 

 dwells at some length on the second proposition. A view somewhat 

 widely held hitherto, is that not only the sperm -nucleus, but also the 

 attendant protoplasm, takes part in fertilisation. The evidence 

 usually adduced in favour of this view Strasburger examines with care, 

 but is unable to accept it as conclusive. On the contrary, in his 

 judgment, his own researches prove conclusively that the cytoplasma 

 of the genei'ative cell in the Gymnosperms, and of the vegetative cell 

 of the Angiosperms, serves only as a vehicle in order to bring the 

 sperm-nucleus to its appointed place, where it is taken over by the 

 cytoplasma of the egg. As already stated, therefore, the cytoplasma 

 of the pollen-tube plays the same part as the cilia in the spermatozoids 

 of the vascular cryptogams. 



The first proposition seems to have been first distinctly formulated 

 by O. Hertwig, and is definitely established by the researches here 

 published. The sperm-nucleus may, in the first instance, differ in 

 size from the egg-nucleus, but it usually attains the size of the egg- 

 nucleus before copulation begins. In the copulating process the 

 nuclei at first become flattened on their apposed sides, the separating 

 walls disappear, and the nuclear cavities blend into one. The nuclear 

 threads come into contact with, but do not interpenetrate one 

 another, so that there is no blending of the substance of the two 

 threads. An actual blending occurs only between the nuclear sap of 

 the tw^o cell-nuclei, and eventually also between their nucleoli. 



Naturalist, 



