No. 460.] STUDIES ON PLANT CELL.—V. 253 
consequently they are not sisters. The two nuclei in the ascus 
then fuse. The origin of the original pair is not known. 
No satisfactory explanation of this fusion in the ascus has 
been advanced. The conditions in the Ascomycetes are not the 
same as in the Basidiomycetes. There is no series of paired 
nuclei in the ascogenous hyphae and no evidence of a delayed 
fusion of gamete nuclei following a sexual act nor of nuclear 
fusions associated with the apogamous development of a sporo- 
phyte generation. On the contrary, a sexual act with the 
fusion of gamete nuclei has been clearly established in some 
forms preliminary to the development of the ascocarp and the 
nuclear union in the ascus is plainly a supplementary phenom- 
enon. Wager and Harper point out analogies to the account of 
Chmielewski (’90b) for Spirogyra, considered in a previous part 
of this section, which described a double nuclear fusion in the 
zygospore. Thus the primary, sexually formed nucleus of the 
zygospore is reported to divide into four secondary nuclei, two 
of which break down while the remaining two unite forming the 
second and final fusion nucleus of the spore. It is hard to see 
how these second nuclear fusions can be sexual and Groom ('98) 
is perhaps correct in considering them superimposed on the sex- 
ual act, but their physiological significance is not clear. 
Some recent papers support in general Harper’s investigations 
on the ascus. Guilliermond (: 04a; :04b) describes the devel- 
opment of the ascus and ascospores in a number of forms. In 
an unnamed species of Peziza he found, however, that the ascus 
developed from the terminal cell of the ascogenous hypha which 
received two nuclei (that fuse) of the four that are found at the 
tip. Maire (:03a; :03b) has reported a similar history for 
Galactinia succosa. Both Maire and Guilliermond note the 
resemblance of these conditions to the nuclear associations in 
the young basidium and Maire does not hesitate to consider the 
two nuclei in the tip of the ascogenous hypha as much reduced 
synkaryons, (paired nuclei) appearing for a very short period 
just previous to the nuclear fusions in the ascus. Maire fol- 
lows Dangeard in denying the sexual processes described by 
Harper in the Ascomycetes and would allign the events in the 
ascus with those in the basidium. Guilliermond agrees with 
