390 DISEASES OF CULTIVATED PLANTS 



year changes to a peculiar greyish-yellow tint, so that in a 

 longitudinal section the wood presents a series of alternating 

 stripes of colour, the larger medullary rays retaining the brown 

 tint longest. The fruit of the fungus eventually appears on 

 wounded branches, or comes to the surface of the trunk in 

 places where the bark is destroyed. 



The form of the sporophore varies much, depending on 

 the conditions under which it is developed. When growing 

 on a large surface, as a trunk it often extends for a consider- 

 able distance without forming a true pileus, but remains as an 

 irregular, flattened patch. When growing on a branch it is 

 often more or less knobbed or lobed, sometimes with an 

 attempt at a stalk, whitish or tinged yellow, 2-3 in. across, 

 upper surface with irregularly notched teeth or spines, edge 

 with club-shaped, sterile teeth, under surface with pointed 

 spines 3-6 in. long. 



Hartig, Die Zersetzungersch. des Hokes, p. 97, pi. xi. 

 Prillieux, Malad. des Plantes Agric., i, p. 321 (1895). 



THELEPHORACEAE 



Sporophore erect and stipitate, partly reflexed or entirely 

 adnate to the substratum ; hymenium even, smooth, and 

 polished, or with projecting cystidia ; spores hyaline or 

 coloured. 



HYPOCHNUS (PERSOON) 



Mycelium forming a loosely interwoven weft spreading 

 over the surface of the substratum. Basidia constantly 

 4-spored, arising in scattered tufts over the surface of the 

 layer of mycelium. 



Differs from Exobasidium in the superficial mycelium, and 

 in the basidia constantly bearing four spores at the apex. 

 Corticium differs in having a compact, waxy hymenium, 

 consisting of closely packed basidia. 



Potato collar fungus (Hypochnus solani, Prill, and Del.) 

 forms a very thin, greyish, or fawn-coloured film round the 

 living haulms of potatoes. This film begins at the point 

 where the haulm emerges from the ground, and extends 

 upwards for three or four inches. It consists of a loosely 



