ALBUGO (CYSTOPUS). 101 
As stated in the foregoing, the process described for A. d¢¢d and 
A. portulacee is paralleled in Pyronema, one of the Ascomycetes. 
A discussion of the process in this genus will form a part of the next 
chapter. 
Fecundation inthe genera Peronospora(Wager, 1900) and Pythium 
(Miyake, ’o1; Trow, ’01) bears a close resemblance to that in Aléugo. 
In the several species investigated, a receptive papilla is formed by the 
oogonium during its development. This papilla certainly facilitates 
in some way the development of the conjugation-tube, which, as all 
the observers state, is formed by the antheridium. In Arazospora 
pulchra’ Thaxter, one of the Leptomztacee, in which the periplasm 
is developed as a peripheral layer of cells surrounding the egg, there 
is some evidence which suggests that possibly the conjugation-tube is 
formed by the oogonium. Wager’s Fig. 4 for Peronospora seems to 
lend support to this view as applied to that genus. 
A central body of differentiated cytoplasm is present in some degree 
in all genera, being more prominent, perhaps, in Aléugo candida and 
Peronospora parasitica, Wager and Stevens have suggested that 
it is functional in bringing the sexual nuclei together, but when it is 
known that in Peronospora parasitica these nuclei separate again 
some distance from each other before fusion, it is difficult to under- 
stand the necessity of such a body unless it is assumed that stronger 
forces are at work in the periplasm which tend to bring all nuclei into 
that region and retain them there, the central body exerting, of course, 
a stronger chemotactic stimulus upon some particular nucleus which 
becomes the egg-nucleus, or, in case of several egg-nuclei, as in A. 
blité and A. portulacee, upon several particular nuclei. During the 
development of the sexual organs in the several species in question a 
mitotic division of the nuclei takes place. In Pythium ultimum 
(Trow, ’o1) the nuclear division in the antheridium may follow a little 
later than in the odgonium, thus giving the impression that a second 
mitosis occurred. The division in both organs seems to be simulta- 
neous in Pythium de baryanum and Peronospora parasitica. Both 
Wager and Stevens have expressed the opinion that the reduction in 
the number of the chromosomes occurs in the antheridia and odgonia,, 
but no decisive evidence is at hand. 
In Albugo candida the sexual nuclei fuse immediately after the 
entry of the male nucleus into the oosphere, and the same is true for 
Albugo portulacee, Peronospora jicaria, P. alsinearum, and P. 
effusa, according to Berlese. In Pythium ultimum, P. de baryanum, 
1 From an investigation made in the botanical laboratory of Indiana University, by Dr. C. A. King. 
