126 Murphy .— The Morphology and Cytology of the 
be considerable, caused by the penetration of the oogonial incept. At 
other times there seems to be another way of attaining this end. The 
antheridium put out a tube of short growth as the pressure caused by the 
oogonial incept increases, the tube acting as a safety-valve. Growth ceases 
as soon as the oogonium emerges. Compare in this respect Pethybridge’s 
figures ( 27 ). This explains to some extent why so many antheridia seem 
when mature to be borne on four hyphae. 
The earliest stages in penetration strongly resemble the formation of 
haustoria as described by several authors, and especially by Smith ( 33 ) in 
the Erysipheae. In Fig. 2 the antheridial wall is deeply invaginated, and it 
can be traced up the side of the developing oogonium until it fades away 
about where the cytoplasm begins. It is not certain that the wall has yet 
been actually pierced, although it may have been. If it has, one would expect 
the tip to be swollen out. The probability is that a very thin and invisible 
sheath of antheridial origin surrounds it. When this is ruptured the 
invaginated wall remains surrounding the stalk of the oogonium and acts 
as a strengthening element, the enclosed part of the stalk being often 
noticeably constricted, as is shown to some extent in Fig. 2i. This is 
exactly what occurs in the formation of a haustorium (Smith, 33 ; 
Gregory, 18 ), although the goblet-shaped collar described by both these 
authors is not present. 
The oogonial incept arises in every case also from a more or less developed 
swelling on a hypha which is applied to the antheridium. This may well 
be compared to the appressoria from which many haustoria develop, as 
de Bary described (compare also Smith, 33 ). It might be suggested, 
however, that this swelling is really homologous with the oogonia of 
other Oomycetes and that the oogonial incept corresponds to the receptive 
papilla (see Fig. 2 ). Against this it may be urged that the appressorium- 
like swelling shows none of the protoplasmic activities of an oogonium- 
Traces of nuclear division may sometimes be seen in the hypha leading 
up to it, but for the most part its nuclei are in the resting condition. 
There is no trace of zonation or of any other phenomena such as would be 
expected at the time when the respective papilla appears. A well- 
developed receptive papilla is formed later on, which seems to rule this 
argument out. 
The comparison with a haustorium, while striking, should not be 
pushed too far. There is no indication that the antheridium thickens its 
wall against the advancing hypha, as the host cell does against the 
haustorium. This has been interpreted as an effort on the part of the host 
to shut out the invader, and obviously no such action would be expected 
on the part of the antheridium. It is part of the normal biology of the 
Fungus. It does seem strange that one part of the organism should react 
in this way towards another part, and yet the same process is duplicated in 
