6o MAINE AGRICULTURAL EXPERIMENT STATION. I9IO. 



certainty exactly what takes place in the dividing nucleus. The 

 same difficulty has been encountered by a large number of in- 

 vestigators who have studied the yeasts and other low forms of 

 Ascomycetes and hence there is much confusion in the accounts 

 given by different writers. 



The young ascus becomes almost spherical in most cases and 

 enlarges to the size of the mature ascus before the nucleus di- 

 vides. After the single nucleus has passed into the rounded 

 part, this portion is cut off by a cross wall. The young ascus 

 contains granular cytoplasm which surrounds a rather large 

 central vacuole. The nucleus as a rule occupies a position in 

 that part of the ascus which is opposite the stalk. The nucleus, 

 in material which is well fixed, shows very much the same struc- 

 ture which as been described for the nucleus of Saccharomyces 

 by Guillermond (4). There is a nuclear membrane, a small 

 amount of chromatin, and a small spherical body which appears 

 to be a nucleolus. This body stains red with the safranin of 

 the triple stain. Unless material is well fixed and carefully 

 stained it is impossible to distinguish the nucleolus from the 

 chromatin and there appears to be a single dense mass inside 

 the nuclear membrane. 



With regard to the method of nuclear division in the ascus, 

 little could be determined. In the first division, figures have 

 been observed which might be interpreted as mitotic divisions 

 with the 'chromatin which is to form the daughter nuclei still 

 held together by the spindle, but the same appearance might be 

 given by the separation of the two nuclei after an amitotic di- 

 vision. 



Four nuclei are produced by a second division and these be- 

 come the nuclei of the 4 ascospores. On account of the extreme- 

 ly small size of the nuclei and of the spores when first formed, 

 it has not been possible to determine the exact method by which 

 the spores are formed. It has been found, however, that the 

 young ascospores are surrounded by an epiplasm as is the case 

 in typical Ascomycetes. The young spores increase in size until 

 when mature they almost fill the ascus. The membrane of the 

 -spore becomes thickened to a rather heavy wall. The '^pore 

 contains a single nucleus. 



The cytoplasm of the developing ascus seems to be of differ- 

 ent composition from that of the mycelium and conidia. If one 

 treats material consistinaf of voung asci, mvcelium, and conidia 



