ALBUGO (CYSTOPUS). IOI 



As stated in the foregoing, the process described for A. bliti and 

 A. portulacece 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 in the genera Peronospora (Wager, 1900) and Pythium 

 (Miyake, '01 ; Trow, '01) bears a close resemblance to that in Albugo. 

 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 Araiospora 

 pulchra 1 Thaxter, one of the Leptomitacece, 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 Albugo 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. 

 bliti and A. portulacece, 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, '01) the nuclear division in the antheridium may follow a little 

 later than in the oogonium, 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 oogonia, 

 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 portulacece, Peronospora ficaria, 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. 



