CHAPTER VIII. THE THALLOPHVTA. 317 



about a fourth of an inch in diameter on dead boughs ; Sphae- 

 ria, which forms small black spots on decaying leaves ; Cordi- 

 ceps, whose various species are parasitic upon the bodies of insect 

 larvae ; and Claviceps, whose species produce ergot on various 

 kinds of grasses. Claviceps purpurea, which constitutes, in one 

 stage of its development, Ergot of Rye, may be selected for more 

 particular description. This fungus begins its development on 

 the Rye when it is in flower, and appears as a tangled mass of 

 delicate threads on the surface of the ovary, also penetrating 

 its tissues. 



These mycelial threads produce numerous conidia imbedded 

 in a yellowish mucus. This is called the sphacelial stage of the 

 development of the Fungus. There then begins to form at the 

 base of the diseased ovary, a dense mass of mycelium, which 

 continues to enlarge until it forms the dense, hard, dark-purple 

 sclerotium, called the Ergot-grain. This is termed the sclerotium 

 stage of development. 



The remains of the upper part of the ovary and the style are 

 often seen attached to the apex of the Ergot-grain, even when the 

 latter is mature, but it very soon afterwards falls off. Sometimes 

 as many as twenty Ergot-grains are produced in a single diseased 

 head of Rye, but more commonly not more than two or three. 

 Each grain or sclerotium consists wholly of a hard and compact 

 mass of mycelium, and contains no part of the original grain of 

 Rye which it has displaced. This sclerotium lies dormant until 

 spring, when, if placed in warm, damp soil, there arise from its 

 interior a number of stalked bodies with globular heads. These 

 are the stromata, and each contains just beneath its convex 

 surface numerous flask-shaped perithecia, each of which con- 

 tains many asci, and each ascus contains several delicate thread- 

 like spores. 



At maturity the asci rupture and discharge the spores, which, 

 if they find their way to the young flowers of Rye, germinate and 

 produce the mycelium, with which this description started, and 

 so the cycle is completed. The successive steps in the repro- 

 duction of this Fungus are illustrated in Figs. 515 to 520 

 inclusive. 



The Discomycetes differ from the rest of the group chiefly 

 in the structure of the hymenium, which is on the surface of a 



