84 BOTANICAL GAZETTE [july 



trichogyne and thence into the ascogone, is essentially as has been described by 

 Harper and others. After the sexual act is completed and the trichogyne is 

 again cut off from the ascogone, many nuclei were observed in the ascogone in 

 pairs. On account of the slight difference in size of the paired nuclei and of 

 the nucleoli,' he believes each pair consists of a male and female nucleus. A 

 fusion of these paired nuclei does not occur in the ascogone, but they enter the 

 ascogonous hyphae in pairs. Brown 25 holds that there is no fusion of the 

 sexual nuclei in the ascogonium. He holds that an appearance quite like fusion 

 results from division of the nuclei, the daughter nuclei remaining closely 

 associated. 



The ascogenous hyphae were observed to develop in several different ways. 

 Whatever the method of their development, Claussen believes that the sexual 

 nuclei and their progeny formed by conjugate division remain entirely distinct. 

 A pair of each of the nuclei finally enters the young ascus, where they fuse to 

 form the primary ascus nucleus. Claussen finds it difficult to make out the 

 structure of the fusion nucleus of the ascus. He is convinced that the first 

 division of this nucleus is heterotypic, and finds a synaptic contraction and a 

 diakinesis, in which there are about 12 bivalent chromosomes. At no point in 

 nuclear division has he been able to distinguish central bodies with certainty. 

 In the second and third divisions of the ascus nuclei he fails to find a synaptic 

 contraction or a diakinesis stage. The number of chromosomes in these 

 divisions is about twelve. The process of spore formation and spore delimi- 

 tation is essentially as described by Harper. 



According to Claussen, the spore, mycelium, and sexual organs constitute 

 the gametophyte, while the ascogenous hyphae represent a sporophyte not 

 sharply separated from the gametophyte. The ascus is a spore mother cell. 

 The sporophyte, instead of having nuclei with double chromosome numbers, 

 contains male and female nuclei in pairs, which divide by conjugate division. 

 The nuclear divisions in the ascus, except the first, have no significance in the 

 alternation of generations in this fungus. — J. B. Overton. 



Cytology 



ntroductory account 



a number of forms 



; of the morphology 



group. The spores in the earliest stages of their formation are uninucleate, 

 but before the spore is mature the nucleus divides and a septum is formed, 



In Amorphomyces alone the septum is not 

 es. The cells of the thallus are character- 



dividing the spore into two cells, 

 formed and the nucleus deerenera 



istically uninucleate, but after the thallus has completed its growth some of the 



2 s Brown, W. H., Nuclear phenomena in Pyronema confluens. Johns Hopkins 



Univ. Circ. 6:42-45. 1909. 



4 



26 Faul, J. H., The cytology of the Laboulbeniales. Ann. Botany 25:649-654 



1911 



