324 REV. GEORGE HENSLOW ON THE 
self-sterile plants are perfectly self-fertile; thus while Verbascum nigrum is quite sterile, 
V. Thapsus and V. Lychnitis are highly self-fertile. Again, though Corydalis cava and 
C. solida are self-sterile, C. Halleri is only slightly self-sterile, and C. intermedia notat — - 
allso. Lastly, while several species of Passiflora are self-sterile, P. gracilis, an annual, is 1 
“ nearly as fertile with its own pollen as with that from a distinct plant.” Secondly, phy- : 
siologically self-sterile plants may themselves become highly self-fertile under certain con- | 
ditions. Thus Mr. Darwin quotes the experience of Kélreuter, who found Verbascum - 
pheniceum to be sometimes self-sterile, at other times self-fertile. Some plants of — 
Lobelia fulgens, according to Gärtner, are self-sterile, others not so; but none of ` 
Mr. Darwin's specimens were in this condition (J. c. p. 179). Eschscholtzia californica is 1 
self-sterile in Brazil, but when introduced into England it became self-fertile. This species, ` 
however, is also much more self-sterile in Germany; and a plant of English parentage | 
sent to Brazil, and exposed for two seasons to that climate, * proved quite self-sterile, ' 
like a Brazilian plant" (l c. p. 333). 1 
These two classes of facts show that physiological self-sterility is only a conditional | 
phenomenon; and probably any usually self-sterile plant will regain self-fertility if — 
grown under changed circumstances, as, for example, was the case with the Brazilian | 
Eschscholtzias described by Mr. Darwin, who says, * their self-fertility had evidently 1 
increased greatly by being reared for two generations in England." 1 
Hence as many of the so-called self-sterile plants become self-fertile in other localities, ] | 
and then, as with Eschscholtzia, show very great vigour, we cannot infer that self-sterility — 
injures the constitution in any way, but is, as Mr. Darwin says, an “ incident ;” for a 
degrees of self-sterility and want of vigour show no necessary correlation whatever, and 1 
the former involves no detriment to the plant beyond the loss of fertility. We may 1 
therefore with tolerable safety, infer that those others which have not yet been shown to — 
be self-fertilizing might become so under proper conditions for evincing such reversion. | 
3. Many plants are morphologically self-sterile. 
Besides physiologically self-sterile plants, there are many of which the pollen of any 1 
flower, although it be quite effectual on the stigma of the same flower, is prevented by cer- - 
tain mechanical obstructions from having access to it, Thus if species of Lupinus have their — 
petals artificially moved, seed is set, but not usually otherwise. Now it appears probable | 
that if such plants be habitually neglected by insects, they will either perish entirely — 
or else become self-fertilizing, or else, as another but more rare alternative, become ` 
anemophilous, as it has probably been with Poferium and Plantago*. The above ` 
appears to have been the case with such conspicuous flowers as Pisum sativum and ` 
Lathyrus. odoratus, which are mostly perpetuated in this country by self-fertilization — 
alone. Phaseolus vulgaris is also highly self-fertile; but P. multiflorus, though closely - 
allied to it, is still morphologically more or less self-sterile. ` 3 
Similarly, certain inconspicuous and irregular flowers, which may therefore be re- d 
* Mr. W. B. Clarke informs me that he has found certain small-flowered species of Combretum to be protero- 1 
gynous, like Plantago, with the style protruding through a circular orifice of the unexpanded flower before the 
stamens appear. = bey i: pod inposita * : 
