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features of tlie tender parent : e.g., Crinum capense when 
crossed with tropical species produces half-hardy offspring. 
The third cause of sterility is the different idiosyncrasy 
which often obtains in plants. By this we mean that 
mysterious “ capriciousness ” that affects certain species, 
which, though closely allied and exhibiting no visible appear- 
ances, either in construction of pollen or elsewhere, that 
would lead the observer to infer any hindrance to fertilization, 
yet absolutely refuse all attempts to blend. In others the 
pollen is effete when placed upon flowers of the same plant, 
but is perfectly capable of performing its duty when used for 
fecundating other species. 
In the genus Hippeastrum ( Amaryllidacece ) “ self-impregna- 
tion is all but impossible, but fertilization between any two 
different members is readily obtained. On the other hand, in 
species of the genus Habranthus , closely allied to Hippeastrum , 
every attempt to cross the several natural sorts has entirely 
failed. Again, in the genus Zephyranthes , closely akin to 
Habranthus, and making seed freely, crosses are obtained with 
much difficulty, and when obtained, are rather disposed to 
sterility” (Herbert).* Similarly Mr. J. Scott has shown that 
Passiflora raxemosa, ccerulea , and alata, “although grown for a 
number of years in the Royal Botanical Gardens of Edin- 
burgh, and annually yielding a profusion of blossoms, have 
never produced a single seed.”f Yet he proves by experiment 
that the pollen of each is perfectly capable of fertilizing the 
others. Other instances could be cited, but these facts seem to 
show something widely different from the two causes of 
sterility mentioned. It would appear that if we suppose such 
groups as Hippeastrum, Habranthus, Zephyranthes, to have 
descended from original stocks, the variation in form has not 
proceeded at the same rate as that “ differentiation of idiosyn- 
crasy ” which is apparently more intimately connected with 
constitutional differences and the reproductive system, than 
it is with external shape ; as is indicated by individuals of 
nearly the same form refusing to cross, while others, more 
distantly connected, breed freely. The well-known discoveries 
of Mr. Darwin with regard to Primula and Linum would seem 
to point in the same direction, though in these, as also in 
Ly thrum, it is not distinct species, but in different forms of 
the same plant, for he has shown that pollen of the long- styled 
form of Linum grandiflorum is useless upon any stigma of that 
kind, though capable of producing the full complement of 
seed in the other form with shorter styles. 
* Journal of the Royal Horticultural Society, Yol. II. p. 10. 1847. 
t Linn. Journ., Yol. VIII. p. 197. 
