32 SCIENCE PROGRESS. 



tions are specially interesting when considered from the 

 point of view of the great dissentience of opinion which exists 

 between most botanists and zoologists as to the nature and 

 function of the nucleolus. Strasburger, who admitted the cor- 

 rectness of Rosen's statements, considered that the difference 

 between an erythrophil and a cyanophil nucleus was largely 

 one of nutrition, and he instanced in support of his view 

 the difference between the erythrophil nucleolus in the 

 nucleus of the well-nourished oosphere and the cyanophil 

 nucleus of the much smaller, and therefore presumably 

 worse nourished generative cell of the pollen tube. But 

 Zacharias, in criticising Strasburger's views, considers that 

 there is no evidence to prove that the one nucleolus is in a 

 better position than another as regards its nutrition, and it 

 is still more difficult to accept the suggested explanation in 

 those cases in which both forms of nucleoli are concomi- 

 tantly present. 



Zacharias has shown that whereas the erythrophil 

 nucleoli contain albumin and plastin, the cyanophil kind 

 (the "pseudo-nucleoli" of Rosen and others) contain nuclein, 

 a substance quite absent from the other class of nucleoli. 

 Rosen in 1892 stated his conviction that his pseudo-nucleoli 

 in reality consisted of chromatic substance (nuclein) and 

 that they contribute to the formation of those remarkable 

 bodies, the chromosomes, which are evolved by the break- 

 ing up of the linin framework after the amount of nuclein 

 has greatly increased in it, previous to the division of the 

 nucleus. Now the nucleolus exhibits striking chancres both 

 during the growth, and also during the division of the cell and 

 its nucleus. As regards the behaviour during cell growth, the 

 relation of the nucleolus to theothercomponents of the nucleus 

 is highly suggestive, and seems to support the view of those 

 who hold that its function is largely, at any rate, nutritive. 



In the embryonic tissue situated at the growing points 

 of plants, the cells are all much alike, differentiation and 

 specialisation only taking place behind these regions. 

 Consequently it is possible to trace the changes which a 

 cell exhibits during its transition from a primitive state to 

 its adult form, and often, further, through the various stages 



