1912] REYNOLDS—PARASITIZED LEAF TISSUE 2277 
cells have a more oblong longitudinal section than the sponge cells 
and are more closely packed. The plants collected were growing 
in a place which was shaded all of the afternoon and part of the 
morning. The collection was made about the middle of July. 
When the leaf is attacked by the rust, the epidermis is broken, 
the palisade is poorly developed, and more or less replaced by 
rounded cells common to the sponge and the diseased palisade 
tissues. In the early stages of the disease the epidermis separates 
from the mesophyll. There is some hyperplasy of the sponge 
tissue. The cells, which remain in the tissue directly under the 
spore beds, are widely scattered 
and separated by the mycelium 
of the rust. When the rust is 
parasitized by Darluca the pali- 
sade tissue is less abnormal and 
disorganized. The chlorophyll 
seems to have largely disap- 
peared from the cells which are 
within the influence of the rust. 
A similar effect upon the nuclei 
is usually seen. An increase in 
the number of nuclei in indi- 
vidual cells was noticed, how- 
_€ver, in tissue just below a peri- 
Fic. 4.—Two cells from Potentilla 
canadensis leaf parasitized by Puccinia 
Potentillae, showing two nuclei in each, 
and in one a suggestion of the beginning 
of an abnormal division of one of the 
thecium of Darluca, which was 
found imbedded directly in the 
tissue of the Potentilla leaf. Fig. 4 shows two contiguous cells, 
each having two nuclei; there is also a distinct deformation of these 
double nuclei. 
6.: PANICUM LATIFOLIUM L.—The cause of the disease upon this 
Panicum is not clear, though it is surely of fungous nature. The 
normal leaf tissue is that of the ordinary grasses. The epidermal 
cells on both sides of the leaf are very large as compared with the 
simple mesophyll cells which occupy the space between the two 
layers of epidermis. In the healthy chlorophyllose cells there is 
only a thin peripheral lining of protoplasm in which the nuclei 
and the chloroplasts are distributed. 
nuclei 
