130 Wager. — Observations on the Structure 
This work was begun in October 1887, in the botanical 
laboratory of the Normal School of Science, at the suggestion 
of Dr. Scott. My first work was done on Cystopus candidus 
and Pythium , and was undertaken to confirm Fisch’s results 
as to fertilisation, etc. Some important facts were obtained 
which tended to show that Fisch’s results were in part 
erroneous ; but owing to the lack of material the work was 
postponed until the following autumn, when I obtained a mass 
of fresh material, which was, however, found to consist almost 
entirely of Peronospora par asitica^ and as this was in excellent 
condition I was induced to work out the details of nuclear 
structure on it, in addition to my work on C. candidus and 
Pythium , which is not yet completed. 
Peronospora parasitica is very abundant on certain cruci- 
ferous plants ; it is very common on the Shepherd’s Purse, 
Capsella bursa-pastoris , where it exists, together with Cystopus 
candidus , in the form of white patches covering the stem, 
leaves, and fruits ; its hyphae ramify in all directions 
through the tissues of the host-plant, sending out numerous 
haustoria, which penetrate the cells, and in many cases com- 
pletely fill them. The haustoria are globular, or short, thick, 
club-shaped expansions, connected to the hyphae by narrow 
basal portions, at the point where they perforate the cell- wall 1 . 
Large numbers of much branched gonidiophores project 
through the epidermis of the host plant. The tips of the 
branches are bifid. The gonidia are large and globose, and 
are borne singly at the apices of the branches. Sexual 
organs, antheridia, and oogonia are found in large numbers 
between the cells of the host-plant. 
All parts of the fungus contain numerous nuclei. They occur 
in the mycelium, in the antheridia and oogonia, and in the 
gonidia or zoosporangia. To obtain preparations showing the 
nuclei, thin sections of the infected plant were cut and stained for 
some time in a dilute solution of haematoxylin, and mounted in 
Canada balsam. Other sections were stained in picronigrosin, 
1 Cf. De Bary, Recherches sur le developpement de quelques Champignons 
parasites, Ann. des Sci. Nat., 1863. 
