I9 i S ] YASUI— DIOSPYROS KAKI 367 



Microspore formation 



There is no marked difference between the primary sporogenous 

 cells and the primary wall cells before the latter begin to divide. 

 Two periclinal divisions give rise to three outer wall layers and a 

 tapetal layer. Two or three successive divisions separate the 

 primary sporogenous cells from the mother cells. At the same 

 time the uninucleate tapetal cells become very distinct between the 

 sporogenous tissue and the wall layers, the latter of which become 

 more and more flattened. 



During the comparatively long resting period, the spore mother 

 cell increases in size, its protoplasm becomes denser (but not so 

 dense as that of the tapetal cells), and the nucleus becomes large 

 (pi. fig. 1). The nucleus contains rather a small amount of 

 chromatin granules associated with the fine linin network, 

 and also a remarkably large nucleolus and several small ones 

 (pi. figs. 2, 3). 



In some cases I observed the larger chromatin granules appear- 

 ing in pairs, but this did not seem to be the usual situation. The 

 reticulum is denser at the outer part of the nuclear cavity than 

 within. During presynapsis certain connections between the 

 chromatin granules disappear, so that the reticulum gradually 

 becomes simpler in structure. At the maximum of synapsis the 

 chromatin substance appears like a mass of granules (pi. figs. 4 

 and 5). 



There is no morphological connection between the chromatin 

 reticulum and the nucleolus, although they seem to occur in very 

 intimate relationship. A great many nucleolus-like bodies were 

 observed close to the chromatin thread, near the large nucleus, but 

 in other cases there was no such relationship (pi. fig. 4). In the 

 presynapsis stage the double nature of the chromatin thread is not 

 clear, but it becomes gradually evident with the loosening of the 

 thread (pi. figs. 6, 7). 



Before 1895, when Moore called attention to the synapsis 

 stage as an important period in the history of the nucleus, this stage 

 was ignored. Since that time it has attracted chief attention, 

 and is regarded in general as an important event in the history 



