254 
Journal of Agricultural Research 
Vol. VIII, No. 7 
spp. than has been suspected. The writer observed this bladder-like 
membrane in Phytophthora cactorum , P. arecae t and P. parasitica . It 
was previously noted in P. parasitica by Dastur (io). Perhaps its 
evanescent nature explains why it had not been previously observed 
in some or in all the forms. 
Considerable difficulty in obtaining swarm spores at will has been 
experienced by previous investigators. By means of the following- 
described method the writer at all times obtained good results: Cultures 
of the various species were made on media known to produce an abun¬ 
dance of conidia, 250 c. c. Erlenmeyer flasks being generally used for the 
;onidia were obtained, a small quan¬ 
tity of sterile water was poured into 
the flask containing the culture, care 
being taken at the same time to pre¬ 
vent contamination. The flask was 
then gently shaken to dislodge the 
conidia from the conidiophores, and 
the suspension of the spores was 
poured into another sterilized .Erlen- 
meyer flask and held at a tempera¬ 
ture of about 15 0 C. At the end of 
from two to five hours a large major¬ 
ity of the conidia had germinated. 
By examining the solution at various 
intervals the different stages of germi¬ 
nation, as shown in Plate 75, were 
readily seen. The length of time re¬ 
quired for conidial germination de¬ 
pends on temperature conditions, as 
shown for P. infestans by Melhus (20), 
who found temperatures below 20° C. 
more favorable for indirect or zoospore germination than the higher 
temperatures. The age of the culture and the temperature at which 
spores are kept are the paramount conditions for germination by means 
of swarm spores. 
The first evidence of germination by swarm spores is the movement of 
protoplasmic granules in the sporangium. In the forms in which the 
vesicles occur the latter appear and enlarge gradually. Careful micro¬ 
scopic examination of a number of condia in different stages of develop¬ 
ment gives the impression that the terminal papillum enlarges and enters 
into the formation of the vesicle or that the membrane which lines the 
inner surface of the sporangium is stretched. The contents of the 
sporangium gradually pass into the vesicle, and after a time the latter 
ruptures and sets the swarm spores free. In many cases the vesicle and 
purpose. 
When an abundance 
s\ 
s\ 
/V 
✓A 
A Cacfbrum 
/\ 
A 
-A 
/\ Infestans 
/A 
— 
a 
Ery throne pi it 
/A 
/\ 
/A 
A 
A Eagi 
/A 
A 
/A 
/N 
S\ Parasitica 
✓a 
/A 
/A 
Synngoe 
/\ 
/A 
A 
/A N/cotianae 
s\ 
a 
A 
A 
A Arecae 
A 
A 
A 
✓-v 
Phoseofi 
A 
A /\ 
A 
/ *\ Faber/- 
A 
/\ 
/\ 
/A Jatrophae 
Fig. 9.—Camera-lucida drawings showing differ¬ 
ences in the shape of the terminal papilla. 
