588 THE FERTILISATION OF FLOWERS. [PART IV. 
self-fertilisation could be dispensed with, and has actually in very 
many cases been lost. Such a result has taken place in the most 
diverse ways, sometimes by dichogamy, sometimes by the position 
of the parts in the flower, sometimes by reversion to the diclinic 
condition. Asparagus officinalis, Ribes alpinum, Rhus Cotinus, 
Lychnis vespertina, &c., are undoubted instances of plants which 
have reverted or are reverting from the hermaphrodite to the 
diclinic condition. 
So when insect-visits were comparatively few it was a step 
towards perfection for entomophilous diclinic plants to become 
monoclinic ; but when cross-fertilisation was insured by sufficient 
insect-visits the reverse transition was advantageous. So is it 
with all other characters which insure cross-fertilisation or self- 
fertilisation. Dichogamy is so general a feature throughout 
whole genera and orders, that it is scarcely possible to doubt that 
it has been inherited as an advantageous character from the 
common ancestors of these genera or orders; but the least con- 
spicuous and least visited species in these groups have reverted to 
self-fertilisation, and in their case this reversed progress has been 
a step towards perfection (cf. Senecio vulgaris, Malva rotundifolia, 
the smaller species of Geranium, Stellaria media, etc.). In 
Rhinanthus crista-galli_ cross-fertilisation in the event of sufficient 
insect-visits 1s insured by the distance of the stigma and anthers 
from one another, and the style is elongated so that its stigma 
must be touched by insect-visitors; but in the less conspicuous 
variety the tip of the style curves backwards so far that self- 
fertilisation ensues without fail. It is needless to cite more of 
the instances already discussed, in which little-visited varieties, 
species, or genera fertilise themselves regularly, while closely-allied 
forms, more abundantly visited, have been able to dispense with 
the possibility of spontaneous self-fertilisation. 
_ In my opinion, if we must describe in general terms the grades 
of perfection in floral mechanisms, we can only call those specially 
perfect which fulfil their purpose in the life of the plant specially 
well; that is to say, which under existing conditions insure the 
sexual reproduction of the species with particular success. We 
cannot admit that either the insurance of cross-fertilisation in case 
of insect-visits, or the unfailing occurrence of self-pollination, is in 
itself a measure of perfection in the mechanism of a flower; for 
both among plants which regularly pollinate themselves and 
among those in which spontaneous self-pollination is impossible 
we find numerous species which prove by their great abundance 
ee 
