8o 



MORPHOLOGY 



the trichogyne. The spermatia have been found attached to the ex- 

 posed tip of the trichogyne, with their nuclei gone; so that discharge 



and nuclear fusion 

 seem to be safe in- 

 ferences. The archi- 

 carp then enlarges 

 and divides, becom- 

 ing transformed into 

 the ascogonium, 

 from which arise the 

 usual ascogenous hy- 

 phae. From hyphae 

 beneath the asco- 



FIG. 190. Anaptychia: section of an apothecium of a 

 lichen, showing the hymenium made up of asci and para- 



gonium the sterile 

 branches arise that 



physes overlying the inner loose mycelium of the lichen body, Droc j uce ffog jnvest- 



and all invested by a thick cortical mycelium, within which \ 



are apparent groups of algae. After SACHS. lg Sterile tlSSUC of 



the ascocarp, the 



whole structure finally breaking through the. surface of the thallus, 

 usually in the form of a disklike or saucer-like ascocarp (apothecium, 

 fig. 190). One ascocarp may involve a single ascogonium or several, 

 just as described under Pezizales (see p. 73). 



(3) BASIDIOMYCETES 



This great group of fungi is characterized by the occurrence of a 

 basidium in the life history. A basidium is the swollen end of a hypha, 

 and consists of four cells or one cell; but in either case it usually gives 

 rise to four slender branches (sterigmata) , and each sterigma cuts off at 

 the tip a spore (basidiospore) (fig. 201). The basidium holds the same 

 place in the life history of a basidiomycete that an ascus does in the life 

 history of an ascomycete. The essential feature of a basidium is that it 

 produces spores externally and that the theoretical number of spores is 

 four. As in the history of the ascus, the young basidium contains two 

 nuclei which fuse. Unlike the ascus, however, the fusion nucleus of 

 the basidium, by two successive divisions, gives rise to four nuclei, and 

 it is these four nuclei that are found in the four spores. In some cases 

 four sterigmata are not produced and four spores are not formed, but 

 four nuclei appear in the basidium. 



