396 REV. GEORGE HENSLOW ON THE 
extremely self-sterile. Whether it has acquired self-fertility in America and New 
Zealand I know not; but it affords a good instance, assuming it to acquire insect aid, 
of an “exception which proves the rule;" for its rivals, Polygonum aviculare and 
Nasturtium officinale, and probably its own exterminator, Hypocheris radicata, or some 
other composite resembling it, as Mr. Travers placed a ? after it, are, as has been shown 
with Dandelion &c., self-fertilizing. On the other hand, the Scarlet Runner failed to set 
seed in Nicaragua, though it “ grew well and flowered abundantly, but never produced à 
single pod ” (Belt's * Naturalist in Nicaragua, p.70). So also did Erythrina and Lupine 
in New Zealand. These are only morphologically self-sterile, and are quite fertile when 
the petals are artificially moved. | 
It is therefore in consequence of their not being visited by the native insects that 
they are thus at an immense disadvantage as compared with introduced self-fertilizers. ` 
19. CowcLusioN. Self-fertilized plants are the fittest to survive in the struggle 
Sor life. 
Iam not single in this belief; for, as has been seen, Mr. T. Meehan has arrived at 
the same conclusion, and I trust, after perusing the successive articles of this paper 
the reader will draw a like inference. 
To sum up the main facts. It has been found that not only are the majority of plants 
self-fertilizing, but that those which are exclusively so propagate abundantly and with 
extraordinary rapidity, flourishing in the most neglected ground and in vigorous com- 
petition, while a number of them have acquired the unenviable reputation of being most 
troublesome weeds, and which become perfectly rampant the moment the hand of man 
is relaxed from keeping them in check. 
Again, they not only propagate with great ease here, but are best able to establish 
themselves in foreign countries, as being quite independent of insects, they run no risk 
of extermination on that score; and lastly, being of a peculiarly elastic disposition, 
capable not only of enduring but flourishing in the most extreme temperatures, fruiti 
freely in the Arctic and Antarctic regions and on lofty mountains in the Tropics. Lastly, 
if the hypothesis which I have advanced be true, that they are all degraded forms, then : 
their ancestral life-history is a longer one than that of their more Seet and | 
intercrossing relations. : 
Hence so far from there being any necessarily injurious or evil effects resulting from 
the self-fertilization of plants in a state of nature, they have proved themselves to be in 
every way the best fitted to survive in the great struggle for life*. 
* Since the above was in type a paper by Kirk is appeared in the tenth volume of * The Transactions of the N. 
‘Institute’ (1878), in which it seems that the danger of native plants being extirpated by introduced species is less 
than was anticipated; that during the last fourteen years they have somewhat lost the extraordinary vigour at first 
exhibited. Nevertheless some have become “troublesome weeds.” These facts quite agree with the conelusi 
expressed in this paper with reference to intercrossing—that as the “stimulus” imparted to [pomea pu 
appeared gradually, but steadily, to decline, so similarly do these foreign weeds in New Zealand, having at first 
received some great stimülus, eem lose it. Nevertheless they have seemingly noi intention of 
"insignificant — jm 
