MOULDS. 391 



and sclerotia, are sometimes present. The mycelial threads 

 branch freely, but the fruit hyphas are not divided into 

 cells (Fig. 56 b). 



The penicillium has fruit organs resembling somewhat 

 those of the preceding group. The fruit hyphae, however, 

 are septate and divide, and each branch ends in a charac- 

 teristic brush-like form. The end of each branch is not en- 

 larged as in the case of the mucor or aspergillus type, but 

 like the latter it is covered by a number of bottle-shaped 

 intermediate spore-bearers, known as basidia. Each of 

 these in turn bears a chain or row of spores or conidia. As 

 many as 8 spores may be held in a row on the end of the 

 bottle-shaped basidium (Fig. 56 c). 



The oidium does not possess a definite fruit organ such 

 as has been described in connection with the preceding 

 forms. The mycelial threads branch and are usually made 

 up of short thick cells. From the ends of the thread or 

 from the ends of the cells, chains of large, oval conidia are 

 given off. On sugar media it will slowly give rise to alco- 

 hol. The odor of limburger cheese may be largely due 

 to the Oidium lactis. 



The moulds, to a certain extent, induce fermentative 

 decompositions(pp. 93, 97). They are of especial interest as 

 the causes of certain diseases in plants, in lower animals 

 and in man. At the beginning of the century, certain 

 botanists held that the blight of wheat and of other plants 

 was due to a microscopic parasite. The first actual dem- 

 onstration of the relation of a fungus to a diseased organ- 

 ism was supplied in 1837 by Bassi, who showed that the 

 silk-worm disease, known as muscardine, was due to a mould 

 Botrytis Bassiana. In the same year the relation of the 

 yeast plant to alcoholic fermentation was for the first time 

 clearly indicated. The possibility of microscopic moulds 



