152 BOTANICAL GAZETTE [ SEPTEMBER 
from material fixed in chrom-acetic acid, cut in serial sections i 
paraffine, and stained on the slide by Flemming’s triple stain 
For full details regarding methods the reader is referred to the 
end of the paper. This investigation was begun in 1897, om 
year being spent in the botanical laboratory of the Ohio State 
University through the kindness of Dr. W. A. Kellerman. Lat 
indebted to Mr. J. H. Schaffner for many courtesies during my 
work at the same institution. Since the summer of 1898 tht 
study has been continued under the direction of Dr. Bradley 
Moore Davis in the Hull Botanical laboratory of the University 
of Chicago, where I have also received helpful advice and a) 
gestions from Dr. J. M. Coulter and the members of the bola 
cal staff. I wish to express my thanks to my wife for much kind 
assistance, in particular for the preparation of Plate XV. 
4 
The character of the mycelium of Albugo varies with e 
nature of the host tissue. The hyphae are slender where tt 
cells of the host are thick-walled and placed close togethe | 
while in loose tissue they may swell to a considerable diamete 
fig. 42 shows the general structure of the hyphae, the roundit 
nuclei, each with a prominent nucleolus and nena. 
distributed irregularly through the vacuolate cytoplasm. * 
single nucleus is represented in fig. rz. It is worthy of atten , 
principally because of its very faint linin network. It has® 
actual diameter of from 2~2. 5M. 
The oogonium may be terminal or intercalary, its 
simply the greatly expanded mycelial wall, as is ev! 
the frequent persistence of haustoria on its surface. ee 
early stages of developing oogonia may be distinguish i 
enlarged mycelia by certain peculiarities of the protoplas® fe 
43.) The nuclei are elongated, the vacuoles are angular al | 
torted, and the cytoplasm is drawn into stringy bands; 
which gives evidence of a disturbance not present in the 0 
mycelium. These peculiarities are frequently evident © 
tative hyphae a distance of 200 from the developing ° 
DEVELOPMENT OF THE OOGONIUM AND ANTHERIDIUM. 
denced 
& 
