234 BOTANICAL GAZETTE [APRIL 
For the purpose of experiment, the light and temperature conditions 
could be easily changed. 
The intumescences were formed very quickly, generally within 
two to five days after covering the plants. Usually they appeared 
on the upper side of the leaf, but were observed also, in cases where 
they were very abundant, on the under side and scattered profusely 
over the upper part of the stem. They did not form on the very 
young growing leaves at the tip of the stem and rarely on the two 
mature lower leaves of the shoot. The appearance of these intu- 
mescences was very similar to that described by VON SCHRENK (Q) on 
the cauliflower. To the naked eye they first appeared as very small 
greenish-yellow dots, projecting slightly from the surface of the leaf. 
These rapidly developed in size, became lighter yellow, hemispherical, 
smooth, and glossy. After about twenty-four hours they became 
whitish and roughened, and projected prominently from the surface. 
Usually the central part of the intumescence was slightly yellowish 
in color, with a ring of more whitish cells around the outside. When 
they first appeared, the intumescences came out over or near the 
main veins; but when very numerous, they broke out all over the 
surface of the leaf and looked very much like incrustations of some 
crystalline salt. The affected leaves curled over toward the under 
side, and this curling became the stronger the more intumescences 
were produced. The single intumescences were from 2 to 3™™ in 
diameter. When formed numerously, however, the single intu- 
mescences often became confluent, making large rough patches. 
These intumescences lasted but a short time; in a day or two they 
had collapsed and become dry and blackened. A cross-section 
through the leaf showed that the intumescences were due to the 
hypertrophy of the cells lying underneath the epidermis. The 
swollen cells were first found in the palisade layer; they elongated 
and pushed against the epidermis; and in most of the cells cross- 
walls were formed. These cells continued to enlarge until the 
pressure upon the epidermis caused it to break and the palisade cells 
to push up through. As the cells enlarged, the chlorophyll granules 
lost their green color, became yellowish, and disappeared entirely 
from the cells or remained very much reduced, scattered through the 
bottom parts. 
