24 Transactions British Mycological Society. 



test of enquiry, there are undoubtedly forms such as Dipodascus 

 which tend to Hnk the Ascomycetes with the lower fungi. As 

 regards the difference between the non-septate hyphae of the 

 Phycomycetes and the septate hyphae of the Eumycetes, this 

 is often unduly emphasised. Many Phycomycetes are not in- 

 frequently septate, e.g. Spinellus in the Mucorineae, especially 

 when the hyphae are old, while in the higher fungi, hyphae 

 frequently remain unseptate during active growth. I would 

 suggest rather that the Ascomycetes were evolved from the 

 lower fungi at some far distant time, long before the present 

 forms of the Phycomycetes existed. The Ascomycetes are clearly 

 of one origin, for the structure of the ascus is so uniform 

 throughout the group that it is inconceivable it could have 

 arisen polyphyletically. Church homologises the ascus with the 

 spore mother cells or tetrasporangia of marine algae. The ascus 

 is clearly a spore mother cell, but to grant this does not imply 

 the phylogenetic connection which Church appears to indicate. 

 Wherever sexuality occurs, reduction in the number of chromo- 

 somes must necessarily follow, this being most readily achieved 

 by nuclear divisions in a mother cell. Just as the fungi are held 

 to have developed along their own sexual lines, so the spore 

 mother cells or asci in the Ascomycetes, are the necessary 

 counterpart of sexual processes. The peculiar development of 

 ascogenous hyphae with their ultimate formation of asci, is 

 a means of enormously increasing the spore output in relation 

 to sexuality and in correlation with special modes of dispersal 

 and nutrition involving tremendous wastage of reproductive 

 units. Again, the basidium of the Basidiomycetes is often held 

 to have no relationship with the ascus. On the other hand the 

 basidium is essentially the same cytologically as the ascus. In 

 both there is a fusion of nuclei followed by a reduction in the 

 number of chromosomes. There are usually three nuclear 

 divisions in the ascus and two in the basidium, but Juel* has 

 recently demonstrated the existence of more than two divisions 

 in the spore mother cells of many Basidiomycetes. In my 

 opinion the basidium can be held to have been derived from 

 the ascus in correlation with a different type of spore discharge. 

 Bullerf has shown that the spores of many Basidiomycetes are 

 violently ejected from the sterigmata. Now whereas in most 

 Ascomycetes each ascus ejects all its spores simultaneously, in 

 the Basidiomycetes each spore is discharged separately from 

 the basidium. If the process of spore formation of a basidium 



* Juel, H. O., Cytologische Pilzstudien, i. Die Basidien der Cantharellus, 

 Craterellus, und Clavaria. Nov. Act. Reg. Soc. Sc. Upsala, ser. iv, iv, no. 6 (1916). 



t Buller, A. H. R., Researches on Fungi, 11. Longmans and Co., London 

 (1922), 



