Mar. 1, 1925 
The Life History of Pilacre Faginea 
411 
together and not spread out indefinitely 
in the. way one finds the mycelium 
producing basidia in Exobasidium or 
Corticium vagum , for example. A true 
peridium is not developed in Pilacre; 
the interlocking and entangling of the 
end branches of the sterile sporophytic 
hyphae make up an outer layer that 
has been called its peridium. 
GAMETOPHYTIC AND SPOROPHY¬ 
TIC GENERATIONS OF PILACRE 
No fungus heretofore described illus¬ 
trates more beautifully than does Pil¬ 
acre the difference which may exist 
between the gametophytic and sporo¬ 
phytic stages in its life history. In this 
fungus the hyphae that produce conidia 
are gametophytic, those producing 
basidia are sporophytic. No conidia 
are developed on the latter kind of 
mycelium. 
The gametophytic hyphae which 
arise from germinated conidia, basidio- 
spores, or from bits of mycelium trans¬ 
ferred to agar plates are of such a deli¬ 
cate structure and so narrow that it is 
difficult to differentiate cytoplasmic 
structures or to determine exactly the 
number of nuclei present in each cell. 
Some of the cells are extremely long 
and no doubt each cell then contains 
several nuclei. The conidia when first- 
formed are uninucleated (pi. 2, C). 
Two masses of chromatin are sometimes 
visible in older spores, suggesting that 
the original nucleus may have divided. 
It is of interest to note that while no 
clamp connections can be found on the 
coarse brown hyphae-bearing conidia, 
these structures are easily found on 
the more delicate pure white hyphae 
which give rise to the basidia. Fixa¬ 
tion of the sporophytic hyphae is ren¬ 
dered difficult by the quantity of air 
entangled in the hyphae of the “perid¬ 
ium.” One occasionally finds cells 
with two nuclei (pi. 2, O). Sometimes 
cells are very long and these probably 
contain several nuclei. The fact that 
nuclei are sometimes found in pairs has 
no sexual significance. It is well 
known that when a fungus nucleus 
divides, the daughter nuclei tend to 
remain close together in pairs and only 
separate when they, in turn, divide. 
The branches that develop into basidia 
certainly arise at the clamp connec¬ 
tion (pi. 2, D and E). The behavior 
of the nuclei at the time of clamp for¬ 
mation has not been followed, and an 
examination of additional material will 
be required in order to determine ex¬ 
actly what takes place at the origin of 
basidium. Presumably, the two non¬ 
sister nuclei which come together in a 
basidium clamp ordinarily fuse without 
further division. Brefeld ( 6) figures 
clusters of basidia in a way which sug¬ 
gests that there may be a great deal of 
proliferation at this time. It is well 
known that in the Ascomycetes a num¬ 
ber of asci may arise as the result of 
such growth. The ultimate cell may 
also fuse with the antepenult, the re¬ 
sulting cell either becoming an ascus or 
by further growth and proliferation in 
turn give rise to another cluster of asci. 
Kniep’s contention (22) that the 
clamps of Basidiomycetes and the cro¬ 
siers of Ascomycetes are homologous 
structures would have been strength¬ 
ened had he cited Brefeld’s figures of 
Pilacre basidia as they arise from 
clamps. Such a suggestion implies that 
one accepts the theory that the Basidi¬ 
omycetes and Ascomycetes have a com¬ 
mon ancestral line. If so, there must 
be some very fundamental reason why 
the basidium becomes 4-nucleated and 
the ascus becomes 8-nucleated after the 
reduction divisions. 
Such stages in the development of 
basidia as are shown in Plate 2, D to I, 
are abundant in sections of the sporo- 
carps. It is clear that the cell wall in 
the middle of the basidium is laid down 
very early (pi. 2, I), even before the 
second division of the nucleus. The 
fusion nucleus, larger than either of the 
nuclei in the pair, is first seen. After a 
second division the nuclei are very 
small, each one containing a relatively 
large nucleolus. Figures obtained by 
the writers show that the basidium in¬ 
creases proportionately less in length 
than in diameter as it matures (pi. 2, 
J to M). It is not unusual to find one 
spore at the tip of the terminal cell (pi. 
2, K). Not infrequently the sterigma 
is found at the side of the last cell of 
the basidium bringing all four spores 
into line (pi. 2, L). In Ascomycetes 
which have fruit bodies of any con¬ 
siderable size, by far the greater bulk 
of the tissue composing the ascocarp is 
gametophytic. The ascogenous hyphae 
proceeding from the ascogonium or 
from the cells which perform the func¬ 
tion of an ascogonium are sporophytic 
in nature, and frequently compose in 
part what is called the subhymenium. 
In cleistocarpic ascocarps the tissue, 
sometimes erroneously called the perid¬ 
ium, which makes up the wall and 
overlies the hymenium, is gameto¬ 
phytic. The peridial hyphae of Pilacre 
are composed of the end branches of 
the hyphae, which are massed together 
below in parallel arrangement to form 
the stipe. Reaching the head, they 
develop the curiously contorted 
branches which, interlocking, form the 
peridium, through which the spores are 
slowly sifted out. As the fruit ages, 
