OKDER PERONOSPORALES 137 



nucleate conidia which are separated from each other by slender connec- 

 tions, the disjunctors, whose dissolution permits the conidia to fall apart. 

 The chains of conidia thus formed raise and eventually rupture the over- 

 lying epidermis, permitting the conidia to escape and to be distributed 

 by air currents. The similarity of these sori, except for the color, to those 

 of Rusts led to the name "White Rust" often applied to fungi of this 

 genus. Upon falling into water the conidia divide internally into several 

 uninucleate, biflagellate, kidney-shaped zoospores which escape by disso- 

 lution of a special spot in the conidial wall. After swimming for a short 

 time these zoospores encyst and germinate by a germ tube. In some 

 species Palm (1932) has shown that the conidia germinate usually by 

 the production of a stout germ tube which infects the host without pro- 

 ducing zoospores. Sexual reproduction takes place in the tissues of the 

 host. Often the portions of the host plant in which this occurs are much 

 hypertrophied. This is especially the case with Albugo Candida in which, 

 the inflorescence and individual flowers of the host may be much thick- 

 ened and enlarged. The distorted flowers remain green and are some- 

 times several times as large as the normal flowers. On the ends of hyphal 

 branches the almost spherical oogones are separated from the hyphae by 

 septa. Stevens (1899, 1901) studied the process of fertilization in several 

 species. The oogone is at first multinucleate, the number of nuclei 

 being as high as 300. These may all pass to the periplasm leaving but a 

 single egg nucleus in the egg or after passing to the periplasm they may 

 divide, half of the daughter nuclei remaining in the periplasm and the 

 other half in the egg so that eventually the latter may contain 100 or 

 more nuclei. The multinucleate antherid on the end of a hyphal branch 

 attaches itself to the oogone and eventually sends into the egg a conju- 

 gation tube through which one male nucleus passes, in the first case 

 mentioned above, or 100 or more in the second case. These male and 

 female nuclei fuse by pairs. The fertilized egg produces a thick wall, con- 

 sisting of a thin endospore and a thick roughened epispore. In the first 

 type of fertilization the zygote nucleus divides repeatedly so that the 

 oospore overwinters as a multinucleate structure. In the spring zoospores 

 are formed and the epispore is ruptured, the endospore pushing out 

 through the break as a bladder which in its turn ruptures and permits 

 the zoospores to escape. Just where meiosis occurs is not yet certain. It 

 has been suggested that the nuclear divisions occuring in the antherid 

 and oogone before fertilization represent this process, or it may occur in 

 the first nuclear division in the fertilized egg. In North America the 

 common species are A. Candida (Pers.) Kuntze, on various crucifers 

 (Brassicaceae) ; A. portidacae (DC.) Kuntze, on purslane {Portidaca ole- 

 racea L.);A. bliti (Biv.-Bern. ) Kuntze, on various species of Amaranthus; A . 

 tragopogonis (DC.) S. F. Gray, on salsify {Tragopogon porrifoliusL.) and 



