ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 59 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including Cell-Contents. 



Structure of Nucleus in Relation to Organisation of Individual.* 

 J. B. Farmer has continued his investigations as to the structural 

 constituents of the nucleus and their relation to the organisation of the 

 individual. While recognising the great importance of the nucleus, the 

 author believes that the properties of the individual may be, at least in 

 part, attributed to the interaction of the nucleus with the cytoplasm 

 external to it. Such interaction of cytoplasm and nucleus is seen in the 

 fact that enucleated eggs of one species of echinoderm, when fertilised, 

 give rise to larva? resembling the male parent. It is also seen in the 

 effects of polyspermy, and it is probable that the reason that polyspermy 

 so seldom occurs in healthy cultures, is that a sudden chemical change 

 results from the entrance of the first sperm into the cytoplasm of the 

 egg. Tlie author has proved that in several Fucaceas and in some ferns 

 the entrance of the first sperm into the egg-cytoplasm is followed by the 

 paralysis or disorganisation of other sperms in the neighbourhood. 

 Evidence that cytoplasm is the cause of similar disintegration is also 

 afforded by the Gymnosperms, and most markedly by the Cycads with 

 motile spermatozoids. 



As to the act of fertilisation, the author considers that not only must 

 there be union of two, and not more than two nuclei, but these nuclei 

 must retain a certain structural basis, and he agrees with Darwin, 

 Weismann, and De Vries in regarding the constituents of the nucleus, 

 and not the nucleus as a whole, as charged with the control of the 

 chemical transformations in the cell, which reveal themselves in the 

 characters of the cell. The chromomeres which constitute the chromo- 

 somes may be compared to ferments which set up in the extra-nuclear 

 cytoplasm, chemical changes which constitute development. The 

 present work favours the Mendelian theory, and it appears that fertilisa- 

 tion is to be regarded as a mechanical mixture of the nuclear 

 constituents rather than the formation of a chemical compound. The 

 units in each of the sexual nuclei retain their individuality, and at 

 fertilisation these units are sorted out into different combinations. 

 Experiments and observations show that the actual number of 

 chromosomes is immaterial, but the usual constancy of number is 

 evidence of the organising function of the cell as a whole rather 

 than of independence of the chromosomes. Chromosome-reduction is 



* Proc. Roy. Soc, lxxix. B (1907) pp. 446-G4. 



