SELF-FERTILIZATION OF PLANTS. 339 
the ovary are highly developed, insomuch that in some of the finer varieties of Pears &c. perfect seed is 
of comparatively rare occurrence; while, on the contrary, in groups attacked by mildew the seeds are in 
general multiplied. In such cases, as the properties which make the fruit valuable are altogether inde- 
pendent of the seed, it is sufficient for the purpose of the cultivator if impregnation have taken place to 
such an extent as to ensure the swelling of the sarcocarp. It is to this abortion that many cases of 
sterility aredue. The process of impregnation is so far successful as to stimulate the contents of the 
embryo-sac and the fleshy walls of the fruit ; but after a time the embryo ceases to grow and the sarco- 
carp withers... . . The sterility is by no means due to deficient impregnation, but apparently to a 
greater degree of heat than its growth requires, which stimulates other parts at the expense of the 
embryo.” 
Mr. Berkeley also remarks, that 
* The influence of the pollen is not the only influence which will cause the succulent portion of the 
organs of fructification toswell. The process of caprification * is an instance in point, as also the touching 
the orifice of a fig with oil, or piercing the young walls with an oiled straw." 
5. Highly self-fertile varieties may arise under cultivation. 
For this important fact I am indebted to Mr. Darwin; and I propose giving under 
this heading a brief summary of certain facts collected from his work on Cross and Self- 
fertilisation of Plants. 
Although in the majority of cases it appears undoubtedly true that the offspring of 
cultivated plants erossed by pollen from a different plant of the same, and still more of a 
different stock, become more fertile than such plants when self-fertilized, yet Mr. Darwin 
raised during his experiment some highly self-fertile forms, which “ yielded more seed 
and produced offspring growing taller than their self-fertilized parents, or than the 
intererossed plants of the corresponding generation." ‘The following examples will illus- 
trate this fact. 3 
In cultivating Zpomea purpurea, with the purpose of contrasting the heights of the 
intercrossed and self-fertilized plants, it was not until the sixth generation was raised 
that a single plant of the latter beat its competitor; that is to say, about forty pairs of 
such plants had been cultivated before one of the self-fertilized surpassed its rival, the 
heights of these two being respectively 87 and 86:5 inches, or as 100:99:4. Mr. Darwin 
was so much surprised at this case, that he saved the self-fertilized seeds of this plant, 
which he called the ‘ Hero,’ and experimented on its descendants, with the following 
results, summarized :— 
(a) Its descendants inherited a power of growth equal to the ordinary intercrossed ; for 
the first generation, i.e. the children of Hero, self-fertilized, were to the intercrossed 
as 100 : 95. 
(b) A cross between the grandchildren of Hero did no good. 
(c) The descendants became more fertile than was usually the case; for the self- 
fertilized grandchildren of Hero had a higher average of seeds per capsule than was 
observed in any other case with self-fertilized plants. 
(d) No benefit was derived from intercrossing with plants of the same stock. 
* Gasparrini, however, denies that caprification has any effect other than impregnation (Journ. Hort. Soc. Lond. 
iii. p. 185). 
