416 
Journal of Agricultural Research 
Vol. XXIX, No 8- 
FERTILIZATION AND MATURATION PHE¬ 
NOMENA 
A striking feature of fertilization is 
the absence of a fertilization tube, 
coincident wit^h the close contact of the 
contracted oosphere with some part of 
the oogonial wall immediately under¬ 
neath the clasping antheridium. But¬ 
ler ( 6 , p. 52) found no fertilization tube 
in a species of Aphanomyces, in which 
the antheridium closely encircled the 
oogonium, but thought it possible that a 
nucleus was transferred before the 
oosphere receded from the oogonial 
wall. He figures a fertilization tube, 
however, in P. vexans, which has the 
same encircling type of antheridium, 
but no close contact of the fused wall 
and oosphere, so far as can be judged 
from his drawings. The close relation 
of oosphere, oogonial wall, and anther¬ 
idium in the species here described 
is brought out clearly in photographs of 
living material just prior to or at the 
time of fertilization. (PI. 4, Aa, Af , 
Ba, Bb, Ca.) Under these conditions 
the direct passage of the antheridial 
contents into the oosphere through a 
hole dissolved in the walls between is 
thoroughly compatible with the clasp¬ 
ing nature of the antheridium, which 
insures sufficient adhesion to eliminate 
the necessity of the anchorage afforded 
by a fertilization tube in species having 
a narrow clavate antheridium. The 
fact that a lateral pressure is exerted by 
the antheridium is well shown by the 
depressed condition of the oogonial 
wall below it, displacing the other¬ 
wise spherical shape of the oogonium 
(Pis. 4, 5, all oospore figures). 
The inception of the exospore wall 
immediately upon fertilization and 
rounding up of the oosphere has not 
been described in detail in this genus so 
far as the writer is aware; most authors 
record the appearance of the complete 
membrane without figuring possible 
intermediate stages. Trow (22) states 
that “the egg rounds itself off and 
appears covered with a membrane 
before the last traces of protoplasm 
leaves the antheridium.” Miyake, 
working with P. de baryanum (18), 
uses similar terms: “Soon after the 
discharge of the antheridial contents 
into the oosphere a thin membrane is 
formed around the latter. This is the 
beginning of the exospore.’ The fig¬ 
ures of both authors show a completely 
encircling membrane of appreciable 
thickness, immediately following the 
highly contracted, smooth-outlined 
oosphere. De Bary noted a thin 
hyaline membrane around the oosphere 
before fertilization in P. de baryanum; 
its first figured appearance is a line 
almost completely encircling the still 
rough oosphere (3, PL I, fig. 3, 4). 
Ward (28), working with the same 
species, states that “meanwhile [during 
fertilization] a very delicate skin had 
been formed over the now smooth 
exterior of the oosphere,” but his 
figures do not show how it was formed. 
The general impression left by these 
authors is of a simultaneous appearance 
of a thin hyaline membrane over the 
entire oosphere. This was not found 
to be the case in the species here 
studied, in which the membrane is first 
visible just within the smoothed 
periphery as a short, narrow hyaline 
strip (really a disk in terms of three 
dimensions) which gradually extends 
tangentially around the periphery until 
the entire oosphere is clothed with a 
narrow, hyaline membrane (PI. 5, C, d t 
e, /)• 
SIGNIFICANCE OF THE PYTHIUM TYPE 
OF SPORANGIAL GERMINATION 
The normal process of sporangial 
germination in this genus results in 
the transformation of the entire spor¬ 
angial contents into zoospores and 
their facile escape through the very 
delicate vesicle wall without any 
waste of zoospore-forming material 
or inherent obstacles to dissemination 
when once formed. It was frequently 
observed, however, that the undiffer¬ 
entiated mass within the vesicle some¬ 
times moved off (as if the bladder had 
been disrupted prematurely), failed to 
differentiate, and degenerated into a 
mass of slime and globules. This was 
frequently correlated with impacts by 
freshly formed zoospores, singly or in 
groups, from near-by sporangia, and 
must unquestionably occur in nature 
through mechanical injury by the 
abundant motile microscopic fauna 
and flora of the soil. Another abnor¬ 
mal condition, observed in only two 
cases, was the disjunction of the pro¬ 
toplasm during its passage through the 
tube; most of it entered the vesicle and 
underwent the usual process, while the 
part broken off and left behind in the 
sporangium failed to emerge, but 
formed a few normal zoospores which 
remained entrapped and finally degen¬ 
erated (PI. 4, H). The rarity of this 
condition in Pythium is indicated indi¬ 
rectly in that incomplete exit of the 
sporangial contents, resulting in en¬ 
trapped zoospores, is neither men¬ 
tioned nor figured in Butler’s mono¬ 
graph (6) nor in Ward’s detailed ac¬ 
counts (23). 
Instances of imprisoned zoospores 
are, however, not uncommon in allied 
genera in which they are completely 
