566 eeport — 1878. 



up as they habitually do, for pollen would then simply be taken from the younger 

 upper flowers, and deposited on the stigmas of those lower down the stalk. In 

 like manner, a similar effect woidd result in the case of proterogynous plants, were 

 these visited exclusively by bees or iusects adhering to the ascending habit of the 

 bee, for pollen would in that case be transferred from the lower older male flowers to 

 the upper female ones, the insect leaving with little or no pollen to carry to another 

 spike. Thus the chances of cross-fertilisation would be minimised, and the ends 

 served by the flower's dichogamy, nectar, and odour would be missed. For these 

 reasons it seems highly probable that proterogynous plants like Scrophularia nodosa 

 are adapted to the visits of insects which do not possess the ascending habit of the 

 bee, but visit flowers when in search of honey in an irregular manner, or in an 

 order exactly the opposite of that observed by the bee, as in the case of wasps 

 visiting Scrophularia before referred to. The lax inflorescence, too, favours an 

 irregular order of visitation, for as the flowers are placed at a distance apart, it is 

 almost impossible for an insect to visit them in perfectly regular order. We see, 

 then, that in both cases things are so arranged that an insect on coming to a plant 

 shall tirst enter a female flower, and there deposit the pollen it brings from other 

 plants, and that before it leaves, whether a bee leaving from the top, or a wasp from 

 the lower flowers, it is well dusted with pollen from the male flowers it last enters. 

 According to H. Miiller, the flowers of Scrophularia are chiefly frequented by wasps ; 

 and S. aquatica Mr. Darwin states to be fertilised exclusively by wasps. It seems 

 only fair to infer that such flowers are in some way specialised to suit the nature 

 and habits of these insects. We have thus got so far with our explanation as to 

 see how plants having proterogynous dichogamy do not have their apparatus for 

 cross-fertilisation rendered ineffectual, as would undoubtedly be the case were the 

 ascending mode of visiting flowers rigidly followed and universal among all species 

 of insects. It still remains to trace the connection of this with obscurity in the 

 flowers, which appear to shun observation almost as distinctly as proterandrous 

 flowers court it. Within certain limits it is an advantage as regards cross-fertilisa- 

 tion that a plant's visitors shoidd be confined to a few or even to one species of 

 insect, for an insect visiting all flowers indiscriminately woidd be likely to have 

 deposited all the pollen taken from a particidar species of flower on the stigmas 

 of other and different species where it would be of no use, before comma- to 

 another plant of the same species as the first. This is probably the reason 

 why the great majority of flowers are visited only by a very limited number 

 of species of insects. Sir John Lubbock gives a list of plants with one species 

 opposite each as its sole visitant ; whether this be really so or not, unmistakablv 

 there is a tendency in this direction. If, then, we find a plant whose flowers secrete 

 nectar, and ascertain that it is visited almost exclusively by certain species of 

 iusects, and if the flowers do not possess a large coloured corolla, we are a,t libertv 

 to conclude that these insects are able to find such plants without its guidance, and 

 that the materials consumed in its production can be otherwise turned to better 

 account in the economy of the plant, just as in the case of self-fertile cleistogamic 

 flowers. Assuming, then, that inconspicuous flowers are adapted to the visits of 

 wasps, is there anything in the habits of these insects different from those of bees 

 that would afford an explanation of the remarkable fact that they appear to be 

 able to discover a small uncoloured flower as easily as a bee can a large and con- 

 spicuous one ? Wasps differ from bees in one important respect, that while the 

 latter are exclusively vegetable feeders, the former add to their vegetable diet by prey- 

 ing on insects smaller than themselves. All through the animal kingdom carnivorous 

 animals are endowed with keener powers of scent and vision than graminivorous 

 creatures. Indeed, it is a direct result of natural selection that a creature whose 

 food is perpetually eluding it should in time acquire acuter perceptive powers than 

 one whose food is more easily obtained. That keenness of vision, then, which 

 enables a wasp to descry its prey at a distance, aided by an acute sense of odour, in 

 all probability also enables it to discover these obscure flowers without the guidance 

 afforded by a large coloured corolla. This obscurity, therefore, specially adapts 

 these flowers for fertilisation by wasps to the exclusion of insects less highly en- 

 dowed in these respects ; while the wasp gains this advantage, that it has an 

 increased chance of finding honey in such flowers on account of the likelihood of 



