PAPERS ON BOTANY 231 
this paper are in the centers of light brown apparently sun- 
burnt areas the two diseases are very similar in appearance. 
STROMATA 
The first indication of the disease is a slight discoloration at 
the point of infection. The mycelium, which is at first hyaline, 
very soon develops an amber-yellow color, the contents of the 
invaded cells disorganize and the infection becomes evident 
through the color changes, even when a very few cells are in- 
volved. “Ihe fungus enters the epidermal cells and shows a 
tendency to grow close to the inside of the walls of these 
cells. From the epidermal region it proceeds into the meso- 
phyll where it reaches its greatest development. Here the my- 
celium becomes dense and the host cells broken down. Per- 
ithecial cavities form in this region, and a dense mass of my- 
celium fills the epidermal cells which were not at first destroyed 
by the fungus, thus forming an incrustation over the stroma. 
In the development of the stromata the perithecia form earlier 
than this covering, and at one stage of the development the 
perithecia are conspicuous under low magnification with trans- 
titted light. The perithecia which in the specimens examined, 
varied in number from two to thirty in a single stroma, occur 
either loosely scattered or so closely compacted that the walls 
coalesce, forming a dense stromatic mass which encloses the 
perithecia. In a transverse section of the leaf the perithecia 
occupy a medial position and the stromata usually fill the leaf 
tissue from one surface to the other before perithecia are 
formed. 
There is considerable variation in size, form, and distribution 
of the stromata. Mature perithecia were seen in stroma as small 
as 0.2 mm. in diameter, An area of one hundred and ninety-five 
square centimeters contained nine large stromata with irreg- 
ular margins, while a similar area contained eighty-one that 
were small, round, and regular in outline. The stromata are 
surrounded by yellowish-brown infected areas forming halos 
which are usually very narrow but may reach a width of one- 
third the diameter of the stromata and are generally a little 
more conspicuous on the under than on the upper side of the 
leaf. 
