300 Ishikawa.—Studies on the Embryo Sac 
which was named pycnella by Atkinson, had flowers like those of Oe. 
pycnocarpa and was very liable to the attack of a kind of Peronospora , 
which was always parasitic only on Oe. pycnocarpa. This one he called 
a segregated hybrid, because it developed to the full expression of certain 
characters selected from each parent. The other, which had petals like 
those of Oe. nutans or somewhat modified by the other parent, he called 
nutanella. This was a blend, since the characters were taken from each 
parent, and an intermediate character of most members appeared in the 
hybrid. Pycnella was quite fertile; its pollen valid for both parents as 
well as for nutanella , pycnella , and itself; while nutanella was self-sterile, 
though its pollen or eggs were perfectly good when combined with those of 
the parent, all other hybrids, and even Oe. Lamarckiana. Some experi¬ 
ments for this self-sterility were undertaken, though it was merely prelimi¬ 
nary. The result is that the pollen grains easily germinate, and the pollen- 
tubes actively penetrate the stigmatic tissues, when the self-pollination 
is carried on in nutanella. The inner morphological aspects of the gameto- 
phytes are quite normal, but the growth of the tube is so sluggish that they 
cannot enter the stylar tissues even in three days after pollination, when the 
ovules show the sign of disintegration. On the other hand, in the normal 
case the pollen-tube gets at the embryo sac in fifty hours; generally the 
ovules of Oenothera begin to disorganize in three days after the flowing 
if not visited by the pollen-tubes, and in such a case some of the embryo 
sacs at times show a sign of disintegration in sixty-eight hours after 
blooming. 
It is interesting to notice that in the hybrids, as in many cases, 
self-sterility is produced owing to the fact that the tube does not grow 
quickly enough to reach the ovule in time for fertilization. As to the cause 
of the feeble growth of the tube we scarcely know any explanation better 
than Jost’s well-known hypothesis (33), namely, £ Moglich ware auch, dass 
auf den Reiz des Pollenschlauches hin nicht Nahrstofie, sondern andere 
Stoffe im Leitgewebe sezerniert wiirden. Die Reaktion miisste auf fremden 
Pollen einfreten, und ihr Erfolg bestande in der Sekretion wachstumsreizen- 
der Stoffe.’ It is also stated by Compton (10) that: ‘ If we compare 
pollination with fungal or bacterial infection it might be expected that the 
result would be the formation of antibodies.’ ‘If there be an analogy 
between fertilization and infection, there is also one between sterility and 
immunity. There seems to be two main methods by which immunity 
is attained. In one the host is constitutionally resistant to the attacks 
of the parasite, this being the more frequent method. In the other the host 
is over-susceptible, and the attack of the parasite produces a quantity 
of decomposing matter which inhibits its further growth. Both these 
methods are paralleled in cases of failure of fertilization.’ 
