THALLOPHTTA— FUNGI 



many the former is much the greater in extent and forms the 

 larger part of the mycelium, being buried in the substratum on 

 which the fungus is growing. In such oases the shoot is com- 

 posed of a few hyphse, bearing the reproductive organs. In 

 other cases the shoot is large and bulky. In some parasitic 

 forms the root hyphse take the form of haustoria, or sucking 

 organs, which penetrate into the cells of the host plant {fig. 819), 

 the rest of the mycelium being found only between the latter. 

 Sometimes, instead of forming a feltwork of mycelium, the root 

 hyphje are gathered into bmadles. The shoot, especially when 

 bulky, is of curious and varied form and never bears anything 

 that can be called a leaf. 



Corresponding with this rudi- 

 mentary morphological differentia- 

 tion, the anatomical structure is very 

 simple. The long chains of cells are 

 produced by ordinary cell-division ; 

 the elongated hyphse grow at their 

 apices ; in the masses of tissue of the 

 more bulky forms a transverse sec- 

 tion shows the appearance of a kind of 

 parenchymatous tissue. It is not a 

 true parenchyma, however, being 

 composed of hyphse which run side 

 by side, cohering together. The 

 outer layers of such a. mass form a 

 kind of cortex, which is more com- 

 pact than the inner parts. Occa- 

 sionally some of the hyphse are 

 modified to form a system of latici- 

 ferous tissue, and a kind of gland is 

 formed in some other species. These 



forms are found generally in the most complex group, 

 Basidiomycetes. 



The cell-walls of the fungi are composed of a modification 

 of cellulose, characterised by not turning blue when treated 

 with iodine and sulphuric acid. This modification, known as 

 fungus cellulose, has recently been shown to resemble in some 

 respects the chitin found in some animal organisms. 



The reproductive structures found m the fungi are very 

 varied. Sexual reproduction is represented in several of the 

 groups, but in others it is unknown, the gametophytes being 

 always potential and not actual. In many a somewhat elaborate 



Fig. 819. Four cells of potato plant, 

 infested with Phytophthora. h. 

 Hypha running* between the 

 cells and sending haustoria, a, 

 into their interior. 



the 



