564 
Journal of Agricultural Research 
Vol. XIV, No. 12 
cells are distributed singly or in little groups throughout the matrix of 
noninfected cells. These groups, the so-called “ Krankheitsherde,” are 
usually entirely separated from each other by noninfected cells. They 
may be either large or small, and the cells that compose them may vary 
greatly in size. 
As sections from the different clubs were studied it became increas¬ 
ingly evident that, in spite of the irregularity in the distribution of the 
parasite, a rather definite relation exists between infected and non¬ 
infected cells. If few cells are infected, the plasmodia become large. 
If many cells are infected, they remain relatively small. Thirty-two of 
the plants studied showed the fungus in the spore stage. This is the 
final stage of the disease and, therefore, the one best suited to a study 
of the relation of the parasite to the tissues as a whole. The observa¬ 
tions of sections from each of the 32 different plants showed that the 
ratio between infected and noninfected cells varies considerably in the 
different clubs. The relation between the volume of the spore masses 
and the volume of the host tissues in which they are embedded seemed 
much more constant. A detailed study has been made of this phase 
of the relation of parasite to host. 
The method used to determine the volume of spores in a given volume 
of tissue was the following. The sections from each club were observed 
under the microscope with low-power magnification, and a careful 
selection was made of a field that seemed to show an average quantity 
of spores for the tissues of that particular club. The section was then 
photographed, and a circular picture was obtained of the field chosen. 
The parts showing spores were then carefully cut out of each photo¬ 
graph. This operation gave many small bits of photographic paper, 
each showing a picture of one or more spore masses. The remaining 
portions of the photograph showed only noninfected cells and those 
parts of infected cells that were free of spores. In this way the photo¬ 
graph was separated into two parts. One part was made up of small 
bits showing spore masses; the other of small pieces showing cabbage 
cells only. The two portions were then carefully weighed on a balance 
and the weights obtained gave the ratio between the area covered by 
spores and the area showing no spores. It was found that although 
different sheets of photographic paper vary considerably in thickness, 
the thickness of different portions of a given sheet is fairly constant. 
Since the spore masses are shown scattered about over the picture, any 
slight variation in the thickness of the paper is not a source of much 
error. The greatest source of error in this method comes from the 
difficulty of following exactly the outline of the spore masses when 
cutting them out of the picture with scissors. By careful cutting, this 
error remains small, and it is believed that the method has given an 
accurate ratio between the area of the photograph showing spore masses 
and the area free of spore masses. This ratio has been determined for 
