220 BOTANICAL GAZETTE [SEPTEMBER 
spores are extremely infectious to sound, green fruit in all stages 
of development. 
Lemons on the tree become infected during the rainy winter and 
spring months, almost entirely on the lower part of the trees (which 
are allowed to branch close to the ground), and in the wettest part 
of the orchard. The fungus at all times shows a very decided 
moisture requirement for its development. Infection takes place 
by swarmspores from the soil, both on the tree and in the washing 
tank, in the latter case by the orchard dirt, dust, leaves, and other 
sediment which accumulates in the water. 
The writers have given much consideration to the generic rela- 
tions of this fungus, particularly as to whether it is sufficiently dis- 
tinct from Pythium and from Dr Bary’s Pythiopsis. It is remark- 
able for the connection which it presents between the Phycomycetes 
of this nature. While similar to Pythium in habit, except as to 
its peculiar parasitism on the lemon, this species is definitely excluded 
from that genus by its internal formation of swarmspores. We 
have felt considerable hesitancy in separating this form from Pythi- 
opsis, on account of the similarity in swarmspore formation; the 
latter, however, being founded on a species of such different habit, 
an entomophthorous form of the Saprolegnieae, and being prac 
tically unknown save from the original description, we feel justified 
in proposing a new genus for our species. It is particularly of 
interest as being more exactly intermediate between the Sapro 
legnieae and Peronosporeae than either Pythium or Pythiops's, 
and also forming a close transition from Pythium to Phytophthora, 
having the swarmspore formation and something of the parasitic 
tendency of the latter. In brief, Pythiacystis has the soil habit 
of Pythium, the aquatic habit of the same and of the Saproleg: 
nieae (including Pythiopsis) except for its usual sterility under 
such conditions, the sporangia formation of Pythium, the swat 
spore formation of Pythiopsis and Phytophthora, and parasitic 
activity intermediate between Pythium and Phytophthora. 
No indication of sexual reproduction has been observed 
large amount of material and numerous cultures examined. 
An Experiment Station bulletin on the nature and control of 
this fungus will be issued in due time. 
in the 
