76 CALIFORNIA ACADEMY OF SCIENCES. [PROC. 3D Ser. 



EXPLANATION OF PLATE X. 



All figures were drawn with the Abbe camera lucida: objective, Zeiss oil 

 immersion 1/12, compensating ocular No. 6, 



Fig. I. A young pollen-mother-cell. The chromatin thread is beginning 

 to break up. The cytoplasm is composed of two elements, one 

 a fibrous network, the other a granular substance. 



Fig. 2. A little later stage. The first row of meshes adjacent to the nuclear 

 wall has begun to pull out. 



Fig. 3. A number of rows of meshes adjacent to the nuclear wall have be- 

 come elongated. The chromatin thread has broken up. 



Fig. 4. The granular substance has begun to collect about the nuclear wall. 

 The outer meshes of the cytoplasm have become radially elon- 

 gated. The nucleolus shows four vacuoles. 



Fig. 5. The granular zone has increased in width. Fibers can be seen 

 between it and the nuclear wall. The linin is thickening up. 



Fig. 6. The granular zone is completely formed. The radial arrangement 

 of the meshes outside of it has disappeared. 



