13 



just "before nuclear division and less than half that 

 just after mitosis. In the older cells tlie average diajn- 

 eter of the nucleus is 2-3 1^ . In tlie young sporelings 

 the nuclei are very small, measuring 1-2 M^ in diajneter. 



The resting nucleus is nearly spherical or smmewliat 

 flattened against the cell wall. It shows a large, densely 

 staining chroxn£itin-nucleobs ir the center. The size of the 

 nucleolus varies from l/5 to 2/3 the diajneter of the nu- 

 cleus. It is smallest at the time of complete rest of the 

 nucleus, and grows larger a.s the time for mitosis draws 

 nea-r. Around the peripher;^ of the nucleus a faint linin 

 network is visible. This is connected \7ith the nucleolus 

 by faint radiating strands (fig. 11). Immediately envel- 

 oping each nucleus is a zone of cytoplasm, which appears 

 denser than the cytoplasm elsev/here, ajad which is probably 

 to be considered of kinoplasmic na,ture. The thickness of 

 tliis zone is omite va.ria.ble. It often becomes a.bout one- 

 third the diajneter of the hucleus. 



ITuclear division occurs regulaj:'!^'' by mitosis, being 

 found most frequently in the terminal cell. It occurs also 

 commonly in the subterminal cell, less comiaonlj' in the 

 third cell from the apex, and ratlier infrequently in cells 

 older than this. 



