74 
JOURNAL OF THE EOYAL HOETICTTLTtmil SOCIETY. 
are branched in rather a compact manner, the tips of the ultimate 
ramnli being mostly ternate, on which are borne the large oval 
conidia. These latter are without papillae at the apex, which 
occur in many species of Peronospora. In size they are variable 
between '0125 x ’0083 mm. and *03 X ’017. The ramification 
and general appearance is very different from that of the Potato- 
mould, perhaps more nearly like that of Peronospora nivea , but 
much larger. 
The observations made by Dr. Parlow on the germination of 
the conidia, or rather the production of zoospores, and their ultimate 
germination, are so important and interesting that they must be 
detailed somewhat in extenso. The experiments were made in the 
beginning of October. Affected leaves were gathered in the after¬ 
noon and kept under a moistened bell-glass during the night. In 
the morning the portions which had developed fresh conidia during 
the night were cut out and the conidia shaken off into a little water 
contained in watch-glasses. In order to test the conditions of 
germination, some of the bell-glasses were placed in a light room 
and others kept in the dark, and sowings were made also at diffe¬ 
rent periods of the day. The result was uniformly the same, 
whether in the dark or the light. Sowings made at any period of 
the day also germinated, but the conidia sown in the morning 
generally germinated somewhat more quickly and more abundantly 
than those sown in the afternoon. This is explained partly by the 
fact that the conidia sown in the morning were in better condition, 
the result of a growth of fourteen or fifteen hours, while those 
sown in the afternoon were the conidia produced during only the 
four or five hours of the forenoon. In all cases the germination 
took place with a surprising rapidity and regularity. At the end 
of an hour the conidia were swollen, and division of their contents 
commenced. At the expiration of an hour and a quarter the 
segments had resolved themselves into a number of oval bodies 
collected towards one extremity of the conidia, and soon afterwards 
the cell wall was ruptured and the oval bodies made their escape. 
They passed out slowly, usually one at a time, pausing a little 
in front of the opening. In a short time each moved more and 
more actively, and finally darted off as a fully-developed zoospore 
furnished with two cilia. Sometimes not more than three 
emanated from one conidium, usually five or six, but in one 
instance as many as seventeen were counted. The zoospores varied 
in length from ’008 to *01 mm. They moved about for from fifteen 
