134 
Journal of Agricultural Research 
Vo 1 . XXIII, No. 3 
December, and March; those of Mindum in October, January, and March; 
and those of Kanred in December, March, and July. The present studies 
are limited to infections on seedlings. 
Material was fixed daily from the time of inoculation until 14 days 
after. The fixing fluids used were the chrom-acetic mixtures, Flemming’s 
medium solution, and several modifications of Bouin’s fluid. The latter 
proved unsatisfactory, in general, although a few fair preparations were 
obtained. Fixing fluids of ordinary strength served for the older tissues. 
Younger seedlings fixed better in solutions made up one-half or three- 
fourths strength. Flemming’s triple stain was the one principally used. 
INVESTIGATIONS 
BAART 
Baart, or Early Baart, is susceptible to the fungus and Mindum is 
somewhat resistant; but, as no differences were observed in the earliest 
stages of their development, two or three drawings of Mindum are included 
here. Drawings other than Early Baart are specified. Only the rust 
found in Berkeley and Puccinia graminis tritici I, were used. 
The wheat leaf is parallel-veined, and over each vein on the upper 
side of the leaf is a small ridge running from one end of the leaf to the 
other, so that this surface of the leaf is minutely corrugated. The stomata 
are regularly arranged in a single longitudinal row on each side of every 
ridge about midway between its crest and the adjoining valley. The 
other side of the leaf is relatively smooth and its rows of stomata are about 
opposite those of the ribbed side. The stomata are all oriented alike, the 
long axis of the stoma being parallel to the length of the leaf. 
The urediniospores were usually placed upon the ribbed side of the 
leaf by means of an inoculating needle and naturally lodged upon the 
ridges at a distance of several cells from the nearest stomata. Many 
of these spores germinated overnight, pushing out germ tubes through 
the pores in the cell wall. The germ tube hugs closely to the surface 
of the epidermis, conforming to the curve of each cell, and regularly 
takes the nearest route to a stoma. Perhaps the water vapor issuing 
from the stoma serves to attract the germ tube, or some faint odor 
diffuses out which acts as a stimulus for a chemotropic reaction. The 
living content of the germ tube flows along as it grows, leaving very 
little behind in the older part of the tube. 
Once the stoma is reached, the tip of the germ tube swells and the 
protoplasm flows into it. It fits closely into the canoe-shaped hollow 
above the aperture of the stoma. When fully formed, the appressorium, 
as this pad or cushion of fungous protoplasm is called, is at least as 
large as the spore from which it came and contains nearly all of its 
living matter. The empty germ tube is now separated from the appres¬ 
sorium by a septum, and its delicate walls soon collapse. It is seen for 
a time as a hazy bluish line but soon disappears. 
By means of this first step in the process of infection, the contents of 
the urediniospore are transferred with the greatest possible economy of 
material to the nearest point of entrance into the host plant. This 
process takes place rapidly, for leaves placed in the fixing fluid on the 
day following inoculation showed dozens of fully formed appressoria. 
The young appressorium contains two nuclei, but older ones regularly 
contain four. Plate 1, A, shows a slightly oblique longitudinal section 
