THE FUNGI 



225 



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a 



into the air. An oogonium arises as a spherical swelling 

 on a hypha, and may be either terminal, as shown in 

 our Fig. 95, or intercalary, i.e. produced at some in- 

 termediate point in the course of the filament. The 

 young oogonium is cut off from the rest of the hypha by 

 a transverse cell-wall. 



Its protoplasm now separates into two parts, a 

 central granular portion which becomes the ovum, and a 

 peripheral layer, lining the cell-wall, called the periplasm. 

 The behaviour of the nuclei has now been made out in 

 several Fungi of this group ; in 

 Pythium, the oogonium at first 

 contains a large number of 

 nuclei, nearly all of which pass 

 out into the periplasm, leaving 

 behind, in the central mass, a 



single nucleus, which is the FIG. 95. Fertilisation of 



functional female nucleus, and is 

 alone concerned in the act of 

 fertilisation and the subsequent 

 development. 



In the mean time the anther- 

 idiuin is formed. It is usually a 

 lateral, club-shaped branch, arising 

 either from the same filament which bears the oogonium 

 (see Fig. 95) or from a different one, and separated from 

 the hypha on which it is borne by a transverse wall. 

 The antheridium directs its growth towards the neigh- 

 bouring oogonium, to which it closely applies itself. 



It may be mentioned here that the mycelium of 

 Pythium and its allies, which is non-cellular during its 

 vegetative growth, generally becomes irregularly parti- 

 tioned up, by a few scattered transverse walls, as the 

 16 



Fythium. A, early stage ; 

 oiigouium (o) and anther- 

 idium (a) still immature. 

 Z>, moment of fertilisation. 

 The contents of the 

 antheridium (a) are pass- 

 ing through the fertilising 

 tube, to unite with the 

 ovum (o). Magnified 800. 

 ( After DeBary.) 



