THALLOPHYTES 



77 



Ergot fungus (Claviceps purpurea). — This is a common parasite on 

 young ovaries of grasses, especially rye. The ascospores infect the 

 ovaries in early summer, and on account of the growth of the mycelium 

 the ovary becomes enlarged and deformed. The mycelium produces 

 abundant sporophores, the conidia being abstricted in clusters, and also 

 excretes copious honey dew, which is sought by insects, and in this way 

 the embedded conidia are carried to other ovaries. 



After the absorption of the tissues of the ovary, the mycelium becomes 

 transformed into a compact, parenchyma-like mass, the sderotium 

 (fig. II 20). These elongated, dark violet, often curved sclerotia, re- 

 placing the ovaries and projecting from the spike, are the so-called 

 ergot, the source of the astringent drug that bears the same name. The 

 sclerotia fall to the ground and pass the winter. In the spring, when 

 the rye is in flower, the sclerotia produce stellate bundles of hyphae, 

 that in turn give rise to 

 long-stalked, rose-colored, 

 globular heads (stromata), 

 in which are numerous 

 sunken perithecia which 

 communicate with the 

 surface through porelike 

 openings. The ascospores 

 are remarkable in being 

 very long and filiform, and 

 are carried by the wind to 

 the flowering spikes. 



Xylaria, which belongs 

 here, is a very common 



183 



184 



Figs. 183, 184. — Xylaria: 183, club-shaped stro- 

 mata arising from the sderotium, the surface perfo- 

 Saprophyte, forming con- rated by the porelike openings of the perithecia; 



<;nirnniiqhflrH black masses '^'*' ^'''=''°" '^""S*" " perithecium, showing asci and 

 SpiCUOUSnarQDlack masses p^j.^^pj^yg^. the ascus wall is so delicate that the row 



on dead wood. From the of ascospores is the conspicuous feature. 



sderotium there arise club- 

 shaped stromata (fig. 183), whose surfaces are perforated by the very 

 numerous porelike openings of the perithecia (fig. 184). 



(h) Laboulbeniales 



This is a remarkable group of fungi parasitic on insects, especially aquatic forms. 

 The sexual apparatus is much lil<;e that of the red algae, the procarp consisting of 

 carpogonium, trichogyne, and auxiliary cells ; and the antheridia producing sper- 



