436 



COMPARATIVE MORPHOLOGY OF FUNGI 



In some species, the formation of a basidium is preceded by a luxuriant 

 conidial formation. In Hypochnus isabellinus (Tomentella flava) (Bre- 

 feld, 1889), there appear in certain parts of the hyphae, numerous lateral 

 branches which, throughout their whole length, cut off a large mass of 

 red-brown, echinulate spores on short sterigmata (Fig. 278). Before the 

 connection of these spores and Hypochnus was known, they were called 



Botrytis argillacea. In Hirsutella varians 

 (Matruchotia varians) the hyaline conidia 

 are cut off over the whole expanse of the 

 mycelium. With the exhaustion of nutri- 

 ent solution, the hyphae collect in coremia 

 which gradually proceed to the formation 

 of "basidia" (Fig. 277). These appear to 

 be connected with conidiophores by a 

 continuous series of intermediate forms 

 (Boulanger, 1893). 



The name Corticium from cortex, bark, 

 indicates the fructifications of all these 

 genera are resupinate, they are directly con- 

 nected to the hyphal tissue of Hypochnus 

 and in these simple forms are thin, mem- 

 branous, at times arachnoid, while in the 

 higher forms fleshy or leathery, and gener- 

 ally attached to the substrate over the 

 whole expanse; thus the cosmopolitan Cor- 

 ticium vagum (C. botryosum, Rhizoctonia 

 Solani), the cause of Rhizoctonia disease of 

 potato and other vegetables, often subter- 

 Fig 278.-Hypochnus isabeiu- sheathing the roots or stems, is 



nus. 1. Hypha with basidium. 2. > » 



Portion of a conidiophore. (X350; hypochnoid. C. salmonicolor (C . javani- 

 after Brefdd, 1899.) cum), which causes serious necrosis of bark 



and twigs of tea, coffee, cacao and cinchona in the tropics, has more 

 luxuriant coverings and a continuous hymenium. In C. Koleroga (Pelli- 

 cularia Koleroga) which causes a thread blight of coffee, the basidia are 

 borne directly on hyphae in mycelial strands covering the under surface 

 of the leaves and extending down the twigs. C. Stevensii (Hypochnus 

 ochroleucus), a thread blight of apple, pear and quince in Brazil and the 

 southern United States, differs in having chestnut-brown sclerotia 3 to 

 4 mm. in diameter and slightly more compact masses of basidia-bearing 



hyphae. 



In genera of the second stage of development, systematic classification 

 is founded on all sorts of artificial characters; thus one places in Corticium 

 (spores hyaline, thus distinct from Hypochnus and Coniophora) chiefly 

 those forms whose hymenia consist exclusively of basidia; in Peniophora 



