378 BOTANICAL GAZETTE [may 
Many of the cells of the diseased area are filled with a homo- 
geneous substance which stains blue, so that at a glance the 
location of the diseased tissue can easily be discovered. The 
protoplasm, which is somewhat more abundant and more evenly 
distributed in the diseased cells than in the normal, is very finely 
granulated. Many of the diseased cells show two nuclei. All of 
the nuclei in the vicinity stain deeper or retain the stain more 
tenaciously than in the healthy tissue, and are relatively larger 
than in the normal cells. The chlorophyll has largely disappeared 
from the cells close to the point of invasion, but farther away the 
Fics. 5, 6.—Cells from leaf of Panicum latifolium: fig. 5, cell from a diseased 
leaf, showing an enlarged nucleus and diminutive chloroplasts; the cell is slightly 
plasmolyzed; fig. 6, cell from an unaffected region, showing a normal nucleus and 
normally sized chloroplasts. 
chloroplasts are merely reduced in size. Figs. 5 and 6 show 
enlarged and normal nuclei respectively; the difference in the size 
of the chloroplasts is easily seen also. 
7. Pyrus Matus L., parasitized by Gymnosporangium sp.— 
The structure of this leaf is somewhat more complex than any of 
those previously described. The upper and lower epidermal cells 
are in single layers, and are partly isodiametric and partly oblong 
in shape. The palisade cells, which are in two layers, have their 
nuclei symmetrically placed in the peripheral protoplasm close to 
the middle of the lateral walls. The chloroplasts are also arranged 
along the same walls. The cells of the upper palisade layer are about 
a third longer than those of the second layer, and are about the 
