278 
Journal of Agricultural Research 
Vol. XXV, No. 6 
The class of ratio values into which the greatest number of conidia 
fell for both strains was 1.25 to 2.14. The average ratio of length to 
width was 1.68 for both strains. While this ratio is somewhat larger 
than the measurements showed in the previous work (7), it is not of a 
sufficient variance, when all other morphological characters are taken 
into consideration, to warrant making a new species for both strains. 
Rosenbaum ( 8 ) in his description of Phytophihora faberi Maubl. gives a 
mean ratio of 1.47 and this figure was more clearly obtained by the 
writer in his previous measurements of the coconut strain (7). Graphic 
representations of the arrangements in classes of the ratio of the length to 
the width of conidia, showing the limits of variation for both strains, are 
given in figures 3 and 4. 
^ Germination of the conidia. —Germination takes place by the pro¬ 
duction of either germ tubes or swarm spores. Every conidium is poten¬ 
tially a sporangium; its method of 
germination is influenced greatly by 
its environment. Germination by 
germ tubes is by far the commoner 
method under cultural conditions. 
From 1 to 5 germ tubes may be pro¬ 
duced ; these apparently may develop 
from any part of the surface of the 
conidium (PI. 10, C). Both strains, 
under favorable conditions, will 
produce an abundance of zoospores. 
These conditions are not clearly un¬ 
derstood. Attempts to produce zoo¬ 
spores from spore suspension of corn- 
meal cultures in sterilized and tap 
water by placing vials containing 5 cc. 
of these suspensions at various tem¬ 
peratures in Altmann regulated in¬ 
cubators from 4°upt0 30°C., failed 
to produce zoospores. Excellent di¬ 
rect germination was obtained. Fre¬ 
quently old oatmeal agar cultures, 
from which the surface mycelium had been removed and then new growth 
allowed to start, would produce zoospores by the addition of water. 
Swarm spores were also obtained in Van Tieghem cells by growing the 
organisms on very dilute agar or in hanging drops of water placed on 
sterile cover slips. Just before formation there appeared a rearrange¬ 
ment of the protoplasmic granules. The swarm spores were then pro¬ 
duced within the sporangium (PI. 11, A and B). The end of the papilla 
finally broke off or was dissolved and the spores escaped. No vesicle 
formation has been observed. The spores approach the opening and 
escape one by one. When produced on dilute agar the zoospores oozed 
out of the sporangium and remained in a mass at the mouth. Here they 
soon germinated by sending out germ tubes (PI. 11, C and D). Fre¬ 
quently zoospores did not escape from the sporangium and then germi¬ 
nation took place within the sporangium (PI. 11, C and D). 
The process of emerging from the sporangium in water cultures is ex¬ 
tremely interesting. After the dissolution of the tip of the papilla an 
active movement of the developed zoospores within takes place. As 
Fig. 2.—Graph showing the variation in width of 
conidia. 
