946 REV. GEORGE HENSLOW ON THE 
constitutional elements, though, as with British weeds in New Zealand, they may acquire — 
by their introduction into new climatal conditions fresh constitutional vigour, superior 
to the native vegetative population; for the White Clover is actually ousting the New- ` 
Zealand Flax, Phormium tenax. Similarly, if the process had been reversed, analogy l 
would lead us to suspect that the New-Zealand vegetation might prove to have the 
mastery in competition, perhaps, with the very same genera and species now growing in ` 
this country. Anacharis Alsinastrum supports this idea. — — E 
Plants which have acquired the property of intercrossing gain immense advantage in 1 
securing the introduction of new constitutional vigour by the infusion, so to say, of fresh | 
blood into their system. And this vigour may show itself in larger foliage, more | 
branches, and therefore more flowers, and in more fruit and seed; but there still 1 
remains a remarkable fact, which Mr. Darwin has shown, that the number of seeds per | 
capsule often remains the same. In some orders and genera this, of course, must be so, | 
as with the Labiate, Boraginee, and Linum ; but it was also true with many others of 3 
which the seeds were nüierous. On the other hand, even with conspicuous plants, several ` 
in Mr. Darwin's experiments became more fertile with their own pollen, though adapted ` 
for intercrossing, as did Mimulus luteus, Ipomea purpurea, and Nicotiana; while Ophrys 1 
apifera produces very large capsules, with an enormous améunt of seed. This last - 
species is clearly a self-adapted form of what represents in other Orchids invariably inter- | 
crossing peculiarities *. Lastly, all inconspicuous self-fertilizing forms, as elsewhere ` 
stated, are great seeders. 
Mr. Darwin says (7. c. p. 386) :— 
“ It seems to me highly improbable that plants bearing small and inconspicuous flowers have been or 1 
should continue to be subjected to self-fertilisation for a long series of generations. I think so, not . 
from the evil which manifestly follows from self-fertilisation. . . . . . . . But, if plants bearing | 
small and inconspicuous flowers were not occasionally intercrossed, and did not profit by the process, - 
all their flowers would probably have been rendered cleistogene, as they would thus have largely benefited — 
by having to produce only a small quantity of safely-protected pollen ” [my italics]. : 
But plants do not pass from one extreme to the other all at once. We do not know - 
all the conditions requisite for producing completely cleistogamous flowers; but as, in ` 
the case of Violets and Oxalis, they are concealed under dense foliage, and with Lamium E 
amplexicaule it is the early and late blossoms, it would appear to be certain external : 
conditions of a lessened amount of light and heat which are requisite. Small flowering ` 
plants, though having flowers more or less approximating the cleistogamous state, are S 
only partially so, because they are still in an intermediate condition from their habit of 
growth, the conditions not being requisite to -reduce them to complete cleistogamy. ` 
Thus Stellaria media and Spergula arvensis wil open in sunshine, but in shade or in ` 
winter are often as completely cleistogamous as Ozalis, —. E 
In the heading to this section I have introduced the qualification ** almost invariably ;” | 
* Great stress is laid by writers on the increased fertility gained by intercrossing. But it must be borne in mind | 
that this increase is relative, not absolute. It is quite reasonable to suppose that plants with conspicuous flowers, and | 
demanding inscct aid, were originally far more self-fertile, and that the increase of fertility gained by intercrossing - 
now only elevates it to the degree it ought to have, and probably had before insect visitation disturbed the sexual i : 
equilibrium. Cn the other hand, the absolute fertility of self-fertilizing weeds is undeniably : 
