CHYTRIDIALES 93 



relative to the growth of the incipient sporangium (Fig. 7 C), so that 

 it may attain a diameter of up to 10.7 \x. Although the primary nucleus 

 does not divide until the sporangium has reached mature size, its first 

 division is quickly followed by others, all of which are intranuclear 

 and synchronous. Average nuclear diameter decreases with each suc- 

 cessive mitosis. While cytological details from her work are given below, 

 for full particulars her publication should be consulted. 



The nucleolus is central, spherical, and about 2 \x in diameter. In 

 some instances the chromatin is collected around the nucleolus, but 

 in well-fixed sections it was more or less evenly distributed. Progressive 

 prophase changes (Fig. 7 D) result in a thickening and shortening of 

 the chromonemata, which are often oriented on the nucleolus; their 

 exact number could not be determined. There was no evidence of pairing 

 as one might expect if the nuclei were diploid. At late prophase the 

 chromosomes lie in the equatorial region with the nucleolus still pres- 

 ent but an intranuclear spindle not yet apparent. In certain nuclei, 

 rudiments of the spindle were seen prior to the arrangement of the chro- 

 mosomes on the equatorial plate, but nothing further of their origin 

 could be determined. 



In the equatorial-plate stages the spindle is broad at the center but 

 tapers sharply at the poles. In several preparations a deep-staining 

 granule was seen at the spindle pole, but, as Karling (1937b) noted 

 for Cladochytriwn replicatum, such granules cannot often be distin- 

 guished from others in the cytoplasm. Hence, it is not certain whether 

 these bodies were actually centrosomes. 



Since chromosome number is important in determining presence or 

 absence of sexuality, special attention was paid to this aspect in both 

 sporangia and resting spores but no conclusion was reached. The 

 chromosomes form a dense irregular band across the spindle (Fig. 

 7 E), an uneven ring in polar view (Fig. 7 H). The density and their 

 minute size made accurate count impossible. In some preparations 

 the equatorial ring appears to consist of from four to six, in others 

 (polar views of anaphase stages) of five chromosomes (Fig. 7 I). 



At anaphase the nucleolus no longer stained easily, but two smaller 

 spherical nucleole-like, ruby-red bodies were evident in the nucleus, 

 presumably nucleoli formed de novo at late anaphase. In Asterophlyctis 



