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 ascogenoushy- 
phae. From hyphae 
beneath the asco- 
FlG. 190. Anaptychia: section of an apothecium of a gonium the Sterile 
lichen, showing the hymenium made up of asci and para- branches arise that 
physes overlying the inner loose mycelium of the lichen body, p ro( J uce 
* 
and all invested by a thick cortical mycelium, within which 
are apparent groups of algae. After SACHS. 
jnvest- 
m g Sterile tissue 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 (sterigmatd) , 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. 
