THE FUNGI 237 



single nucleus, though in some allied Fungi the cells are 

 multinucleate. The mycelium, as already mentioned, 

 forms a dense web on the surface of the leaf; its hyphse 

 cross and touch each other at many places. 



2. KEPRODUCTION 



It is at the points where two hyphse cross or come 

 into contact that the fruits originate. Each of the ad- 

 joining hyphse sends out an upright branch ; the one 

 enlarges and becomes club-shaped, and is cut off by a 

 transverse wall ; the other remains more slender, comes 

 into close contact with the former, and grows up with it, 

 soon overtopping it and bending over its apex (Fig. 97, A). 

 Two transverse walls are formed in this second branch, 

 one near its base, and the other higher up. 



Of these two organs the former, i.e. the club-shaped 

 branch, bears the name of the ascogonium, for it is from 

 it that the ascus ultimately arises. The most recent 

 investigations have proved that the second organ is really 

 an antheridium, and that a true act of fertilisation takes 

 place, a point which had previously been much dis- 

 puted. According to the investigations referred to, 

 fusion takes place between the ascogonium and the 

 terminal cell of the antheridial branch, the cell-walls 

 between them disappearing. Then the nucleus of the 

 antheridium passes over through the opening and unites 

 with the nucleus of the ascogonium. In the case of 

 Sphcerotheca and its nearer allies these facts are now well 

 established, so it is evident that, in these Ascomycetes at 

 any rate, the development of the ascus-fruit is preceded 

 by a sexual process quite comparable to that of the 

 Oomycetes (cf. p. 225). 



