NOTE 
MORPHOLOGY AND CYTOLOGY OF THE SEXUAL ORGANS OF 
PHYTOPHTHORA ERYTHROSEPTXCA, PETHYB. (PRELIMINARY NOTE). 
— -The Fungus which forms the subject of this study, as first recorded and described 
by Pethybridge 1 (1913), has a peculiar arrangement of the sexual organs in that the 
antheridium, instead of growing up by and becoming laterally adpressed to the 
oogonium, is pierced by the developing female organ, which then grows through it 
and, rupturing the wall at the opposite side, emerges and assumes a spherical form. 
These observations have been confirmed and amplified, and the cytology has 
been worked out. 
The antheridia arise first as intercalary swellings, rarely terminally, and they are 
cut off by septa. The hypha in the act of giving rise to an oogonium may be seen 
not infrequently while still within the antheridium, having pierced one wall, but before 
it emerges at the opposite side. When it emerges it is at first club-shaped, but it 
quickly becomes spherical and grows to full size. In every case in which the con- 
nexions could be traced the male and female organs are borne on separate hyphae 
but the Fungus is homothallic. 
When the organs are full grown the stalk or lower part of the oogonium lies 
within the antheridium. A section in the direction of the long axis of the stalk shows 
the latter in or on the antheridium, and a section at right angles to this direction 
shows the stalk lying free within it — a small circle within a larger one. There is no 
trace of the antheridium growing around the base of the female organ when the latter 
is fully grown or nearly so. 
The oogonium, when mature, is filled with dense protoplasm in which are 
distributed a number of nuclei, which are first elongated and irregular in shape, but 
afterwards round off and appear to increase in size. About two-thirds of them then 
gradually disintegrate and disappear. At this time a thick plug is formed in the stalk 
of the oogonium. 
Meantime the protoplasm of the oogonium has become less dense and less 
deeply staining, and the remaining nuclei, now larger and in the prophase of division, 
arrange themselves in the form of a hollow sphere with one in the centre. In this 
position all pass through a normal mitosis. The stages of the prophase, origin of the 
spireme, chromosome formation, and migration to the nuclear plate, are very clear. 
The spindle is intranuclear, but the membrane soon disappears. Centrosomes are 
present. The chromosome number is small but is very difficult to estimate with 
certainty, though it is probably about five. The oogonial nuclei undergo but a single 
simultaneous division. 
1 Pethybridge, G. H. : On the Rotting of Potato Tubers by a New Species of Phytophthora 
having a Method of Sexual Reproduction hitherto undescribed. Sc. Proc. R. Dublin Soc., vol. xiii 
(N.S.), 1913, No. 35, p. 529. 
[Annals of Botany, Vol. XXVIII. No. CXII. October, 1914.I 
