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1903] * PRIMARY NUCLEUS IN SYNCHVTRIUM 4^9 



The nucleolus follows the growth of the nucleus, enlarging 

 to a diameter of about 14^. Nucleolar inclusions in the form 

 of homogenous globules of varying size imbedded in a granular 

 matrix are more abundant than in earlier stages, A single cell 

 of Synchytrium divested of its host envelope is exhibited in fig, 

 2. The nucleus has not yet reached full size, but is typical of 

 this stage of development. It shows well the thick nuclear 

 membrane, the peripheral chromatin, the connecting strands, and 

 the nucleolar inclusions. Fig. j shows a single more mature 

 nucleus drawn to a larger scale. Here the chromatin is arranged 

 in lumps, massed largely on one side of the nucleolus, while the 

 inside of the wall is thickly beset with chromatin-bearing 

 globules. The nucleolus is still more granular and the inclosed 

 globules more numerous than in earlier stages. The whole dark 

 central portion of the nucleolus must be interpreted as a vacuole, 

 which, together with the increasing number and size of imbedded 

 globules (dissolution products) , indicates the disintegration 

 of the nucleolus, a change further emphasized in fig. 4, where 

 the nucleolus is almost entirely converted into the characteristic 

 vacuoles. This change in the nucleus is the first visible sign of 



approaching mitosis. 



f^^ 



4, a large and remarkably clear area may be seen between the 

 nucleolus and nuclear membrane, evidently a large vacuole 

 created by the characteristic aggregation of the chromatin. 



Up to this time the nuclear membrane has been sharp and 

 distinct, even thick, the nucleolus large and conspicuous, the 

 chromatin in irregular masses partaking in no way of the 

 appearance of threads, and a large intranuclear vacuole has been 

 constantly present. 



All of this now changes. The membrane becomes gelatinous, 

 the chromatin assumes a spireni form, and the nucleolus disap- 

 pears. The nuclear membrane, previously thick and definite, 

 first loses sharpness on its outer surface and is no longer to be 

 seen as a definite wall. Dissolution begins from the outside. 

 The nuclear region is long maintained, clearly mapped out, being 

 now bounded by a layer of gelatinous consistency which stains 

 more darkly with the orange G than does the surrounding 



