ON THE SEXUALITY OF THE FUNGI. 287 



If a spore germinates in the neighbourliood of a living hypha 

 of I sari a, however, the germinal tube fixes upon the Isaria 

 hypha and at once emits more tubes, which are thicker and 

 more vigorous than before. If the germinal tube from the 

 Melanospora spore comes within a certain maximum distance 

 from a branch of Is aria its apex grows directly towards the latter 

 until a union is effected.^ This was observed and confirmed 

 several times. All the above facts are generally true of the 

 conidia also; and Botrytis may be substituted for Isaria as 

 the host plant. 



After about eight days the above processes have resulted in 

 the formation of a vigorous mycelium and the formation of 

 young perithecia. The perithecium commences by the de- 

 velopment of a lateral branchlet, which becomes coiled two or 

 three times, and divided by a few septa; this is the ascogonium. 

 It frequently resembles that of Ascobolus. 



Thinner hyphal branches now spring from below the 

 ascogonium, and envelope it by applying themselves closely 

 to it, and branching and dividing; although one of these 

 may grow out more rapidly at first, it does not seem 

 to more than hint at an antheridial branch. But very 

 often two or more arise together, and others soon follow in 

 all cases. 



None of these branches copulate with the ascogonium. 

 Although Isaria branches may be close to and serve to nourish 

 the hyphae producing the fructification, there is no doubt what- 

 ever that only the hyphse from the Melanospora enter into 

 the constitution of the fructification. 



The details of the development of the perithecium wall from 

 the enveloping hyphae are interesting, but present nothing 

 essentially new, and need not be described here. 



Of the four or five cells into which the coiled ascogonium is 

 divided, the cell below the apex forms the ascogenous tissue. 

 The terminal cell above it becomes disorganised ; it is sterile, 



1 Cf. my description of the behaviour of a hjpha of Pythium gracile, 

 'Quart. Journ. Mic. Sc.,' October, 1883, p. 504; and also the remarks below 

 on the behaviour of Spirogyra in conjugation. 



