Humaria rutilans, Fries. 
4 * 
A little later the beak reaches the periphery of the mass and the 
outline of the latter is defined, in section, by a line passing in both 
directions away from the centrosome (Fig. 48). Frequently this line 
cannot be traced to the lower part of the spore, and this portion appears 
to be delimited by the sides of neighbouring vacuoles. The wall of the 
spore becomes increasingly definite and the nuclear beak continues to 
elongate, remaining attached to the inner membrane of the spore (Fig. 49). 
The nucleus then becomes rounded up and the beak disappears. 
One or two vacuoles are always enclosed in the spore plasm, and 
become very conspicuous in the mature spore. They contain oil. 
Abnormalities. Certain abnormalities in the development of the 
ascus are fairly common ; trinucleate (Fig. 50) and tetranucleate (Fig. 51) 
asci are sometimes formed ; their fate could not be determined. In three 
or four cases asci were found containing .two nuclei, each a good deal 
smaller than the ordinary definitive nucleus, and each undergoing synapsis 
(Fig. 52), and, in one case, a single nucleus of ordinary size was seen in which 
the contracted thread was aggregated into two separate masses (Fig. 53). 
Occasionally after the second division, and more rarely after the first, 
two of the nuclei in the ascus undergo fusion (Fig. 54). It seems probable 
that such asci degenerate ; they were never observed at a later stage of 
development. 
Two or more nuclei are sometimes observed within one spore (Fig. 55), 
binucleate spores being of fairly common occurrence. 
Sexuality of the Ascomycetes. 
The most important of the earlier work on this subject is due to 
De Bary ( 14 , 15 ), who described the sexual organs of Sphaerotheca , Asper- 
gillus and Erysiphe. From these and similar discoveries he inferred that 
a sexual process was of general occurrence among the Ascomycetes. In 
1884, however, in view of his own and his pupils’ more extended work, he 
( 16 ) reached the conclusion that, while some of the Ascomycetes are 
undoubtedly sexual, yet others are parthenogenetic, the archicarp being 
present but developing without ordinary fertilization, or apogamous, the 
sexual organs having entirely disappeared. 
These conclusions have been largely borne out by subsequent dis- 
coveries. 
Harper ( 27 ), in 1895, observed the fusion of the sexual nuclei in 
Sphaerotheca and in 1896 in Erysiphe. The former discovery, contradicted 
by Dangeard ( 12 ) in 1897, was subsequently confirmed (Blackman and 
Fraser (6)) in 1905. 
In 1900 Harper ( 30 ) described the coenocytic ascogonium and an- 
theridium of Pyronema and the fusion of the numerous sexual nuclei 
in pairs. 
