ato. mo.] KUWADA.—A CYTOLOG. STUD. OF ORYZA SATIVA. 277 



usual with the free nuclear divisions, and after the emb^osac 

 has been lined with free nuclei, the wall-formation begins. In 

 the later stage of development the nuclear division is sometimes 

 not accompanied by the wall-formation. Thus there may be 

 found two nucleated cells (Fig. 24). The both nuclei finally 

 come to fuse, and make a syntriploid nucleus. I have once 

 observed the mitotic figure of these double nuclei, in which the 

 two spindles were visible (Fig. 25). 



Summary. 



Maiosis in the development of pollen-grains. In 

 the young stage of the pollen-mother-cell, the chromatin-masses, 

 nearly as many as the diploid number of chromosomes, are 

 scattered in the nuclear cavity, each two forming a pair. 



The chromatin-masses stretch out into the double threads 

 somewhat with an appearance of pearl-strings. 



They enter the chief contraction stage of synapsis. But the 

 double nature of the threads can be still clearly made out in 

 thin sections cut 2 fJ. thick. 



The conglobed threads begin to become loose and at last 

 stretch themselves over the nuclear cavity, where the double 

 threads unite together to form simple threads. Thus the con- 

 jugation of chromatin-threads does not take place in the con- 

 traction stage itself, but after this stage has passed over. 



After a while the separation of the united threads takes place. 

 Then the segmentations occur, and 12 double segments or 

 gemini make their appearance. 



Thus through all stages of prophase, the paired arrrange- 

 ment or union of chromatin-threads or chromosomes is formed 

 by parallel association, not by an end-to-end association, viz. 

 the process is a parasyndesis, not a metasyndesis. 



They become shorter and thicker, and assume a dumb-bell 

 shape or a somewhat square shape. 



In the prophase of the division the nucleus is usually pro- 

 vided with several dwarf-nucleoli beside the ordinary large one. 



The behavior of chromosomes in the homotype division is 



