MOLDS AND YEASTS AND DISEASES CAUSED BY THEM 235 



rye and develop a mycelial mass which grows in the utricle, dis- 

 placing the grain, the rudiment of which lies above the mass of 

 the mold. Closely packed conidiophores produce oval conidra 

 and at the same time secrete a sweet milky fluid which attracts 

 insects and thus furthers the distribution of the parasite. Later 

 the mycelial mass produces sclerotia, which are masses of thick- 

 walled cells containing starch and oil together with specific poi- 

 sonous substances, and the whole becomes dry and hard with black 

 outer covering, forming the ergot grain, which is considerably 

 larger than the normal rye grain. In autumn this falls to the 

 ground and remains until spring, when numerous red stalks grow 

 out of it. Upon the swollen ends of these stalks, abundant as- 

 cospores are produced, and these serve to infect again the flowers 

 of the new crop of rye. 



This fungus is of great importance as the source of the drug, 

 ergot, and as a cause of food poisoning, ergotism, in certain coun- 

 tries. It is one example of a mold parasitic upon higher plants. 

 There are very many different species of such parasitic fungi, 

 and they are probably the best known microbic agents causing 

 diseases of plants. 1 



Botrytis Bassiana. This mold was shown to be the cause of 

 muscardine, a disease of silkworms, by Bassis and Audouin in 

 1837, a discovery following closely the recognition of the itch 

 mite, Sar copies scabei, as the cause of scabies in 1834. The in- 

 fected silkworm becomes sluggish and dies, and the aerial hyphae 

 of the fungus grow out from its surface and pinch off round or 

 pear-shaped conidia. These spores gain the surface of other 

 silkworms or butterflies by contact or by air transmission, and 

 germinate, sending threads into their bodies. Sickle-shaped 

 spores are produced from these inside the body, and these grow 

 out into, threads, forming a mycelial network throughout the 

 body of the victim and causing its death. It is possible that 



1 For a consideration of molds in relation to plant pathology, see Massee, 

 Diseases of cultivated plants and trees, New York, 1910. 



