Feb. 12, 1917 
Studies of the Genus Phytophthora 
261 
of the contents of the antheridium passing through a definite fertilization 
tube into the oogonium; and following its passage, the consequent 
changes in the growth of the oogonium into that of the oospore takes 
place. 
Phaseoli group. —In this group the antheridium, which is not club- 
shaped, but approaches the form of a flattened sphere, is produced at 
the base of the oogonium; but no fertilization tube can be observed. 
After fertilization the antheridium remains attached to the oosphere, 
and there is very little, if any, change in its contents. In this group are 
included P. phaseoli , P. arecae , P. erythroseptica , P. parasitica, P. colo- 
casiae , and P. infestans (?). These are shown in Plates 76 and 77. In 
reality this should be called the li infestans group,” as P. infestans is the 
oldest described member, but in the opinion of the writer it has not yet 
been conclusively shown that the method of fertilization in P. infestans 
is the same as in the other members of the phaseoli group, and therefore 
it can logically be placed in the faberi group. In all the other members 
of this group the antheridium develops first and persists throughout the 
life of the oospore, which is not yet proved to be the case in P. infestans . 
All previous investigators agree on the general absence of antheridia 
even in cultures showing all stages of development of the oospore-like 
bodies, and the author has confirmed their observations. In the few 
cases where antheridia are apparently present it is hardly safe to say 
what is the exact method of fertilization. For still other reasons given 
in subsequent paragraphs, it seemed best to designate this group as 
above, P. phaseoli being second as regards age since its description. 
Faberi group. —In this group the antheridia are entirely unknown 
either in artificial culture or on the natural hosts. It may also include 
forms in which if the antheridium is present its position, whether basal 
or side, is not known. It is a tentative group and contains forms which 
may be subsequently transferred to the other groups. As a result of the 
present study, it includes P. faberi , P. jatrophae , and P. nicotianae , as 
shown in Plates 76 and 77, the last form, according to Pethybridge, 
probably belonging to the cactorum group. 
Until recently the only method of fertilization in species of Phytoph¬ 
thora was that found in the cactorum group, and, as explained, it consists 
of a fine light thread, or tube, sent out from the antheridium into the 
oogonium and through which a part of the contents of the former passes 
into the latter. Following this, the oogonium changes into an oosphere 
and finally into an oospore. In the forms placed in the phaseoli group, 
however, a new method of fertilization was recently observed. Clinton 
(7), in speaking of the antheridia and oogonia of P. phaseoli , writes: 
For a long time it was difficult to decide whether or not these threads did not actually 
penetrate the antheridium and grow through it, and we are not yet certain that this 
does not soinetimes occur. Certainly the optical effect is frequently that of an internal 
thread, with its apical wall very thin as compared with the side walls. * * *. . In 
