20 MICROBES, FEEMENTS, AND MOULDS. 



III. ASCOMYCETES; ERGOT OF RYE; THE MOULD OF 



LEATHER AND DRIED FRUITS. 



In distinction from the species just described, the 

 fungi in this group possess endogenous spores, enclosed 

 in a sac or special envelope which is called an ascus ; 

 hence the name of the family. Truffles, or Tuberacece, 

 are only reproduced by the . spores contained in these 

 asci; but most of the other ascomycetes present in 

 addition several forms of spores, and the phenomenon 

 of alternation of generations has led to the belief that 

 in this case, as in that of the foregoing group, many of 

 the so-called species are only successive transformations 

 of one and the same species. This is the case with 

 the ergot of rye, a product used in medicine; it is, 

 however, a serious and dangerous disease of several 

 of our cereals, and particularly of rye (Fig. 8). 



Ergot is caused by a minute parasitic fungus which 

 attacks the ear of rye when it is in flower. The 

 young flower is covered with a white mass, consisting 

 of microscopic spores, formerly termed sphacelium 

 (Fig. 9). These spores reproduce themselves on other 

 flowers, and propagate the evil. 



The mycelium formed by the germination of the 

 sphacelium affects the grain, forms in it a thick felt- 

 work, and is developed so as to constitute the elongated 

 substance termed sclerotis (on account of its hardness), 

 or ergot ; it is called at this stage Claviceps purpurea. 



