128 Murphy.—-The Morphology and Cytology of the 
cannot be recommended. It is mentioned because, later on, the mycelium 
in the tube begins to fruit, but the fruits never reach maturity, while 
mature fruits are abundant at both ends. The abortive oogonia are in 
part brown, or surrounded by a brown exudation, reminiscent of the 
abortive oogonia of P. infestans (Pethybridge and Murphy, 30 ) ; in part 
they are merely empty and colourless. This is no doubt due to lack of 
oxygen, at least in the case of P. eiythroseptica. The fructifications of the 
latter, even in plate cultures, are all near the surface. 
In both these ways several cultures were obtained which were certainly 
the product of a single hypha. These were planted together on set plates 
in the way that Blakeslee has made familiar, and the first results obtained 
tallied so closely with his that it seemed certain that we were dealing 
with a heterothallic form. Fructifications appeared thickest along fairly 
regular lines separating the different growths, while later they appeared 
all over the plate. This might have been due to the intermingling of 
hyphae of different strains, but it was not. The single-hypha cultures 
also fruited when grown alone. The explanation is this : While vigorous 
growth is taking place (up to a certain limit) there is no fruiting ; but 
when growth is suddenly checked in any one place fruit bodies are 
immediately formed along that line. This happens when two growths 
meet, the first consequence being a more or less regular line of sexual 
organs along the junction. Exactly the same effect may be produced 
by cutting out a piece of medium in the track of growth of a single 
strain. No doubt the same thing occurs when two species of Phytophthora 
are grown in the same plate, as Clinton ( 10 ) did with P. Phaseoli and 
P. infestans and claimed to have obtained hybrids. Few details are given, 
but it is possible that what happened really was that the sudden check 
experienced by the slow-growing P. infestans was just what was needed to 
stimulate it to normal sexual activity. 
Further Growth of the Sexual Organs and Degeneration of Nuclei 
before Division. 
Both sexual organs in the early stages are filled with dense, almost 
homogeneous, but slightly granular and vacuolate protoplasm, which stains 
deeply with gentian violet. The nuclei, particularly in the oogonium, are 
linear for the most part (Fig. 13). They are in the resting condition, but 
it is difficult to stain them to show details beyond a nucleolus, which is 
always present. There is good evidence that they multiply mitotically 
in the hyphae about to form an oogonium. The nuclei of the antheridium 
are more nearly spherical. After the young oogonium emerges from the 
antheridium growth takes place with extreme rapidity. Pethybridge saw 
one grow to about the stage shown in Fig. 13 in about four hours and 
