92 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Uostowzen found that in the plant he was examining:, the conidia 

 formed zoospores or they germinated by a tube. He places it under 

 a new genus, Pseudoperonospora, and, as it differs slightly from the 

 species cubensis first described by Berkeley and Curtis, he designates 

 it as var. tweriensis. 



Studies on the Fertilisation of Albugo Lepigoni and some 

 Peronosporeae.* — W. Ruhland records the results of his research on 

 several forms of Oomycetes. Albugo Lepigoni grew on Spergida marina ; 

 the oogonia developed rather plentifully towards the end of the vege- 

 tative period. In the young oogonium there are some 60 to 90 nuclei 

 present. These increase in size and the first mitosis takes place, 

 simultaneously in the oogonium and the antheridium. The chromo- 

 somes, about four or five in number, were extremely small and evidently 

 round in form. At a further stage the nuclei wander towards the 

 periphery of the oogonium ; other divisions must take place though 

 they were not followed in detail, but the number of nuclei increased to 

 o00 or 450. The latter stages of division show a much smaller spindle. 

 Meanwhile the ccenocentrum had appeared towards the centre of the 

 oogonium. It absorbs the surrounding plasma and increases to a rela- 

 tively large size. The female nucleus attaches itself to the ccenocentrum, 

 and after division and degeneration of the resulting daughter nucleus 

 it is joined by the male nucleus from the antheridium, and both enter 

 the ccenocentrum, which gradually disappears as the nuclei increase in 

 size. They show a very fine spirem stage, then fusion takes place and 

 subsequent division, the dividing nucleus resembling the first karyo- 

 kinesis in the oogonium, with the same number of chromosomes. By 

 repeated division, some seventy to eighty nuclei are formed, and the 

 oogonium becomes surrounded by a thick exospore formed from the 

 periplasm. 



In Peronospora Alsinwrum the nuclei of the oogonium divided only 

 once, and the " period of zonation," when all the nuclei had travelled 

 to the periphery, lasted a considerable time. A ccenocentrum appeared 

 here also. Fusion of the two nuclei was delayed for a considerable 

 time till after the exospore was formed, 



ficlerospora graminicola provided an immense number of oogonia. 

 These contained few nuclei. The spindle formed in mitosis was very 

 large, and the chromosomes had a U shape. Xo ccenocentrum was 

 present, and probably owing to this the male nucleus remains for some 

 time at a distance from the female nucleus. The different stages are 

 described in detail. 



In Plasmopara densa the development largely resembles that of 

 iSderosjwra. There is no ccenocentrum, and in both forms the periplasm 

 is drawn into the oospore, and the exospore is consequently of a slighter 

 structure. 



The writer concludes by reviewing the work done on all the forms of 

 Albugo. He finds a regular gradation of forms from Albugo Bliti, in 

 which a large number of female nuclei fused Avith male nuclei, to 

 A. Lepigoni, where only one is present. The receptive papilla is also 



* Jahrb. Wiss. Hot., xxxix. (1903) pp. 135-6G (2 pis.). 



