OMPHALIA FLAVIDA 407 



The head is an oblate spheroid (a flattened globe) with an 

 apophysis of smaller diameter below (Fig. 205, A, B, C). Its upper 

 surface is slightly depressed in the centre. The apophysis encloses 

 and clasps the stalk about 0-1 mm. from its extreme end. The 

 head is tough and coriaceous, so that, when it dries, it is not appre- 

 ciably deformed. With moderate magnification one can observe 

 that the main oblate-spheroidal part of the head, but not the 

 apophysis, is covered peripherally with a large number of aerial 

 radiating hyphal filaments (Fig. 205, C, /). It is these filaments 

 which serve to infect a new host-leaf when a head has fallen upon it 

 and the weather is sufficiently moist. 



The stalk is a solid cylinder (Fig. 205, B, C, D), and not hollow 

 as described and illustrated by Puttemans.^ When very young, it 

 is quite straight and perpendicular to the substratum (Fig. 212, 

 A, B, p. 419) ; but, as it grows in length, it usually becomes more 

 or less bent or curved (Fig. 205, A and B). At maturity, i.e. when 

 about 2 mm. long, it is thickest at its base, slightly attenuated 

 from its base up to the apophysis and then, within the apophysis, 

 distinctly contracted and always more or less sigmoidally bent 

 (Fig. 205, B and C). The sigmoid terminal portion of the stalk is 

 hidden from external view inside the head, but can readily be 

 observed after the head has been removed from it. 



The microscopic structure of a median-longitudinal section of 

 the head and upper part of the stalk of a mature stilbum-hody is 

 shoM^n in Fig. 205, C. The head consists of a central mass of 

 relatively large pseudoparenchymatous cells (m), surrounded above 

 and at its sides by a thin layer of smaller and more flattened cells 

 from which radiate outwards a number of slender branched septate 

 hyphae (n) which, at the sides of the head, terminate in large pear- 

 shaped cells (k) and, at the top of the head, terminate in more 

 slender clavate cells {i). A certain number of the swollen cells at 

 the sides of the head give rise each to a single aerial hypha which is 

 usually simple (1) but may be branched. The hyphae grow out- 

 wards from the head and give it the woolly appearance that can be 

 seen externally with moderate magnification. The clavate cells on 



^ Puttemans {loc. cit., p. 159, Plate XI) in his Fig. 4 erroneously shows aerial 

 hyphae just as thickly present on the top of the head as at the sides. 



