KUNKEL: ORANGE RUSTS OF RUBUS 565 
the writer is unable to explain why infection did not result. The 
experiment should be repeated. 
After being fully convinced that the orange rust, so common 
around New York City, is functionally different from the one in 
New Hampshire a special effort was made to discover possible 
morphological differences between the two forms. Infected plants 
from the two sources were placed side by side and carefully com- 
pared. Special notice was taken of the color of the spores in 
mass, the size and distribution of the Caeomas, the effect on the 
host, etc. Material of both forms was fixed in Flemming’s weaker 
solution, embedded in paraffin in the usual way, sectioned with a 
microtome and studied under the microscope. Spermogonia 
are abundant in both cases. Their form, size and distribution 
was noted as well as the size and shape of the spermatia. In 
both forms the aecidiospores are born in chains with intercalary 
cells. The spores from the two sources were compared as to size, 
shape, content, thickness of spore wall and spore wall markings. 
Fifty ripe aecidiospores from the New Hampshire material were 
chosen at random and measured along their greatest diameters. 
The average diameter for the fifty spores was found to be 25.25 u. 
Fifty aecidiospores of Caeoma nitens were likewise chosen and 
measured in the same way. Here the average diameter was 
found to be 25.29 u. The difference obtained is not great and 
may well be attributed to errors in making the measurements. 
This comparative study has failed to disclose either macro- 
scopic or microscopic morphological differences between the two 
tusts. So far as the writer has been able to observe both are 
exactly alike morphologically. Only after having germinated the 
spores is it possible to distinguish between the two forms. 
DISCUSSION 
The close morphological and pathological similarity between 
two apparently different rusts at once raises the question as to 
whether or not they are genetically related. Do we have here a 
case of parallelism or has one of the Caeomas been derived from 
the other? It is possible to conceive that two rusts living on the 
same hosts may after a time show similar morphological char- 
acteristics, but it is hard to think they would become so much alike 
