CHAPTER V. — COMPARATIVE REVIEW.— ASCOMFCETES. 



227 



formed closely woven thallus-structures (see page 43), which cause roundish red 

 spots about 1 cm. in diameter in the still living green leaf; spermogonia and archicarps 

 make their appearance in the spots in the course of the summer. The Fungus does 

 not go beyond the complete development and subsequent fertilisation of the archicarps 

 during the summer, but falls to the ground in autumn with the leaf, and there the 

 further development of the perithecium takes place, if the conditions are favourable, 

 at the expense of the reserve of food in the thallus ; the spores become ripe in the 

 ensuing spring. The process can of course be to some extent hastened or retarded 

 in plants under artificial cultivation by changes in the temperature and in the supply 

 of moisture. 



The sclerotia of Claviceps pxirpurea and its nearest allies (see section VIII) mature 

 during the summer and remain dormant all the winter ; in the next spring each 



FIG. 108. Claviceps purpurea, Tul. A sclerotium which has given rise to seven 

 stromata. B upper portion of a stroma in median longitudinal section ; cp perithecia. 

 C highly magnified perithecium divided through the middle with the surrounding 

 parts; cp orifice, sh cortical tissue, hy inner tissue of the stroma. D ascus isolated ; sfi 

 ascospores issuing. After Tulasne from Sachs' Lehrbuch. A natural size. B slightly, 

 C and D highly magnified. 



FIG. 109. Claviceps purpurea, 

 Tul. Ascospores germinating 48 

 hours after being scattered on 

 water. Magn. 375 times. 



sclerotium, if it happens to lie on moist ground, usually produces several spherical stalked 

 stromata (Fig. 108 A), the upper spherical portion of which is thickly covered with 

 perithecia sunk half-way beneath the surface (B. C). The ejected cylindrical filiform 

 ascospores (D) swell in different parts under the influence of moisture, and put out 

 germ-tubes at several points (Fig. 109). If the ascospores of Claviceps have found 

 their way into young flowers of the Gramineae (Secale in artificial cultivations) under 

 conditions favourable to germination, their development begins in the pistil, according to 

 Kuhn's observations, and doubtless after the germ-tubes have penetrated into the pistil, 

 though this has never been directly observed. The young pistil concealed between 

 the paleae is first of all traversed in every direction and enveloped by a luxuriant 

 growth of the hyphae of the Fungus, as has been already described : a white hymenium, 

 Leveille's Sphacelia, then forms on the whole of the furrowed surface, and from cylindrical 

 sterigmata on it gonidia are abscised (Figs, no, 111 a). During the formation of 



Q 2 



