4 



96 DuGGAR : Development of the Pot.len Grain 



found a few spherical chromatic masses at definite points on the 

 linin, staining deeply with tlic gentian. 



Under the lower powers the cytoplasm has a granular appear- 

 ance, and under very high magnification it is very closely netted. In 

 Bignonia the cytoplasm is very dense, and as a consequence kino- 

 plasmic radiations or fibers are not so readily distinguished, and 

 probably some effects, especially in later stages of division, 

 thus obscured. 



are 



Synapsis 



On passing into the condition of synapsis, Fig. 20, the linin frame- 

 work is somewhat thicker than in the resting: condition. I have ob- 



served no double row of chromatic granules nor any indication of 

 fission previous to the contraction of the thread. As usual dur- 

 ing synapsis the contracted linin mass stains poorly, taking the 

 orange diffusely. The coils of the contracted mass arc not en- 

 tirely obscured by the density of the ball, but the diffuse staining 

 renders problematical any full account of changes that may occur 

 during this period. 



The nucleolus is at one edge of the contracted thread, and 

 from the optical periphery there are one or more projections on 

 its surface. Several so-called vacuojes ma)' be seen in the middle 

 part, but these also often represent projections, sometimes swollen, 

 leading to linin attachments. Sometimes these structures are re- 

 fractive. In this stage the nucleolus of the tapetal cells shows 

 some signs of disintegration, and upon its surface there appear very 

 large and refractive clear spaces. These undoubtedly enclose air 

 in some way, and b}' long treatment with xylol and alcohol, as sun- 

 gested by Zimmcrmann,* or even with treatment by xylol alone, 

 these vacuoles largely disappear. They disappear at least so far 

 as the air present is concerned, but certain clear spaces remain as 

 before, showing no special refractive. power. 



TJie Spirem Stage and Segmentation 



No indication of a true spirem is seen until after synapsis, and 

 the initiation of this spirem is marked by a stronger reaction to the 

 stains. At first the spirem consists of a loose, slightl)- thickened 



* Zimnicrmann, A. Morphologic uikI riiysiologie des Zellkernes, 41. 



