Phenomena and Problems of Self-Sterility. 199 
Morgan has carried out a series of experiments on Cionn intestinalis 
with the object of locating the seat of the phenomenon and 
assigning a proximate explanation. He concludes that “ immunity 
of the egg to its own sperm is due to the failure of the sperm to call 
forth in the egg of the same individual the reaction that leads to the 
absorption of the spermatozoon. The failure to self-fertilise is a 
specific reaction that takes place or fails to take place at the surface 
of the egg itself ” (1910, p. 233.) 
In the higher plants, owing to the complexity of the mechanism 
of siphonogamy and angiospermy there are a great number of 
theoretically possible causes of self-sterility. The most extensive 
study that has been made of the subject is that of Jost (1907). The 
result of his experiments is to show that the cause of the failure to 
fertilise in the case of self-sterile plants (Corydalis cava, Secale 
cereale , Liliutn bulbiferuni) is concerned with the passage of the 
pollen-tube through the style. Since the growth of the pollen-tubes 
is entirely inter cellular, it follows that the chemical substance 
responsible for furthering the growth (whether by means of nutrition 
or of stimulation) or for hindering it, must be soluble and diffusible : 
but no artificial culture medium was discovered in which pollen- 
tubes could grow to nearly the extent necessary to produce fertili¬ 
sation. 
Pollen-grains, like fungus spores, can germinate on many culture 
media, and, as Strasburger has shown (1886), on the stigmas of a 
great variety of plants of distinct species. But the full growth 
necessary for fertilisation can only result under a very limited set 
of conditions. 
It may be remarked that the feeble growth of pollen-tubes in 
the stigma in cases of self-pollination may have the same cause as 
their failure in artificial culture: and that this may be similar to 
that which Morgan found in Cionn, viz., the failure to evoke the 
necessary reaction from the tissues of the style. This may indicate 
that the soluble diffusible substance in question acts in a positive 
manner, by furthering the growth of pollen-tubes in xenogamy. 
111.— Analogy with Immunity. 
On the other hand, the analogy with the phenomena of immunity 
to which Jost calls attention, leads to the opposite conclusion, 
we compare pollination with fungal or bacterial infection it might 
be expected that the result would be the formation of anti-bodies. 
The work of Schiff-Giorgioni (1905) on Bacillus olece, and of Bernard 
(1909) on the Fungi which inhabit the roots and tubers of Orchids, 
