DIV. i THALLOPHYTA 437 



the classification and phylogeny of which there is still much un- 

 certainty. The attempt has been made to derive them from the 

 Phycomycetes. Not only is the construction of the thallus against 

 this, but the structure of the sexual organs and. the development of 

 the fruit in the Ascomycetes indicate on the other hand a connection 

 with the Red Algae. The Uredineae or Rusts, one of the simplest 

 orders of Basidiomycetes, appear to connect the latter group with 

 the Ascomycetes. 



The saprophytic or parasitic thallus of the Eumycetes is, like that 

 of the Phycomycetes, composed of fine, richly-branched filaments or 

 hyphae which together form the mycelium (Fig. 66). The hyphae are, 

 however, in this case septate, consisting of rows of cells. The cell 

 membrane, which contains chitin, is usually thin. In the colourless 

 protoplasm there are usually numerous minute nuclei (Fig. 6), 

 while in other cases each cell has a pair of nuclei or only a single 

 nucleus. Chromatophores are wanting and true starch is never 

 formed ; the place of the latter is taken by glycogen, often in con- 

 siderable quantity, and by fat-globules. The hyphae of a mycelium are, 

 as a rule, either isolated or only loosely interwoven ; they spread 

 through the substratum in all directions in their search for organic 

 nourishment. In many of the higher Fungi, however, the profusely- 

 branching hyphae form compact masses of tissue. Where the fila- 

 ments in such cases are in intimate contact and divided into short 

 cells, an apparently parenchymatous tissue or PSEUDO-PARENCHYMA 

 is produced. Such compact masses of hyphal tissue are formed by 

 some species of Fungi when their mycelia, in passing into a vegetative 

 resting stage, become converted into SCLEROTIA, tuberous or strand- 

 like, firm, pseudo- parenchymatous bodies, which germinate under 

 certain conditions (Fig. 36). In the fructifications the hyphae are 

 also nearly always aggregated into a more or less compact tissue 

 (Fig. 37). 



The two sub - classes are distinguished by their respective 

 methods of asexual spore-formation. The ASCUS is characteristic of all 

 Ascomycetes ; it is a club-shaped sporangium within which a definite 

 number of spores (usually 8) is formed in a peculiar way by free cell 

 formation (Fig. 381). The Basidiomycetes have in place of the 

 ascus a BASIDIUM of varying shape. It may either be four-celled or 

 a unicellular tubular structure from which the spores are abstricted by 

 a process of budding in definite numbers, usually four (Figs. 398, 403, 

 410). 



Sub-Class L Aseomyeetes (*> 51 > 52 > 61 ' 74 ) 



The Ascomycetes in their typical forms possess sexual organs, 

 the oogonia, which here go by the name of ascogonia or, as in the 

 Red Algae, of carpogonia, and antheridia. The sexual organs have 



