185 



cells arising from the ordinary yeast-globules, in which subglobose 

 bodies were produced by free cell-formation, and which he there- 

 fore regards as sporidia, and the cells in which they appear as 

 asci. The sporidia, Avhen set free from the asci, again gave origin 

 to ordinary yeast cells ; but in no case did mycelium threads, 

 similar to those of the moulds, proceed from the yeast cells, or 

 the sporidia. The results were therefore only negative, which 

 might arise from a faulty mode of cultivation ; nor could he fairly 

 assume that Penicillium had no connection with yeast, and that 

 tlie facts recorded by more successful observers were unworthy of 

 credit. 



Brefeld has, on the other hand, traced the growth of Penicillium 

 glaucum to a higher stage ; and if his observations are correct, 

 has shown it to possess a second and sexual form of reproduction. 

 I shall endeavour in few words to explain his views. 



He considers that the bodies observed by Rees were not true 

 asci, as they did not proceed from any process of conjugation. 

 His experiments are important, as they tend to modify the theory 

 of polymorphism, which has been carried to a great length by 

 various writers, as Hallier and Hoffman among Germans, and 

 Trecul and others among the French. As, in most such cases, the 

 theorj- is doubtless true to some extent, but has been carried too 

 far, and without sufficient proof, in others. 



Polymorphism supposes that several forms, generally considered 

 to constitute distinct species, and even genera, are in reality only 

 phases in the development of a single individual. This has been 

 affirmed to a great extent of Penicillium glaucum ; and in order 

 to test its truth, Brefeld isolated some of its conidia, and carefully 

 secluding them from the access of the air, which might convey 

 the spores of other species, subjected them to a long course of 

 cultivation. He sowed them on various substances, and in different 

 solutions ; but obtained the most satisfactory results from spores 

 sown on coarse, unfermented bread (Entwicklungsgeshichte, p. 

 52). After 14 days he found a dense, creeping mycelium had 



