igoS] NICHOLS— POLLEN OF SARILiCEXIA 



35 



lead irresistibly to the conclusion that the formation of the chromatin 

 is intimately connected with nucleolar activity. The relations of the 

 nucleolus and the chromatin in the prophases of the first maturation 

 division again plainly suggest an elaboration of chromatin by the 

 nucleolus. The fact that at this time the nucleolus stains purple, 

 whereas ordinarily it stains red with the safranin and malachite-green 

 combination, indicates that a chemical change of some sort is taking 

 place within it. The globules of material thus elaborated escape into 

 the nuclear sap, there to be absorbed by the linin and distributed along 

 its threads. Gregory (2) was led to a somewhat similar view by his 

 study of the pollen development in sweet peas. His observations 

 indicate that ^'the nucleolus receives and stores the bulk of the chro- 

 matin during the resting periods which intervene between successive 



mitoses. 



?> 



The varying observations concerning the behavior of the nucleolus 

 give rise to the opinion that it has not the same definiteness of function 

 as the chromosomes and centrosomes. Since there is certainly an 

 exchange of material between cjioplasm and nucleus, and within the 

 nucleus progressive and regressive changes in chemical constitution 

 of its contents, it would seem that a rounded body staining unlike 

 chromatin and therefore designated nucleolus might frequently arise, 

 but representing at different times and in different cells a different 

 physiological acti\ity. The precise nature of the metabolism of the 

 cell, it is natural to suppose, varies according to the kind of cell and 

 the species of plant or animal, and therefore the nucleoU may be 

 expected to vary in appearance and in their relation ta the chromo- 

 somes or other constituents of the cell. That this may be the case in 



animals has been demon 



McGiLL (4) 



'O 



s. In some forms appar- 

 the use of the chromatin 



In 



and thus granules and irregular masses occur within it. 

 perhaps the material is not greatly transformed in the nucleolus, 

 passes out into the nuclear sap there to be absorbed and utilised 

 the chromatin. In the latter instance the connection between 

 nucleolus and the formation of chromatin would be difficult 

 demonstration. Thus such evidence as is gi\-en by Dcjbles" (i) of 

 non-participation of the niicleolus in chromatin formation is negal 



