THE FUNGI 237 



single nucleus, though in some allied Fungi the cells are 

 mulfcinucleate. The mycelium, as already mentioned, 

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

 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 disputed. 

 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 disap- 

 pearing. 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 some of its 

 allies these facts are now well established, so it is evident 

 that, in many Ascomycetes at any rate, the development of 

 the ascus-fruit is preceded by a sexual process quite com- 

 parable to that of the Oomycetes (cf. p. 225). In other 

 cases reduced forms of sexual fusion occur, comparable to 

 those observed in apogamous Fern-prothalli (see p. 77). 



