L26 



KNOWLEDGE 



"JUNB, 1901. 



an- ply supplied iu all such aueinopliilous or wind-ftiti- 

 lized flowers. 



This plan of wind-fertUization. however, which was. no 

 doubt, that employed by all the primitive flowering 

 plants, and is still used by a very large number of them, 

 possisses disadvantages which are sufiiciently conspicuous. 

 There is an enormous waste of pollen, because even under 

 favourable conditions, for ona grain which reaches the 

 stigma of another flower of the same species, perhaps a 

 hundred, perhaps a thousand, peihaps ten thousand, 

 find other resting-places ; and in inclement weather the 

 waste of pollen must be prodigious. It is quit« clear, 

 therefore, that a gi-eat advantage would be gained could 

 some means be devised for the direct and more certain 

 conveyance of pollen from flower to flower ; and this 

 medium of communication is supplied by certain insect 

 visitors. The attraction that led the insects to the 

 flowers in the first place was no doubt this same pollen 

 which thev used, and which many still use. as food. 



Wind-fertilized plants (Reed-mace, Typ}ia latifolia, and Eeed 

 Jloadon -grass, Gli/ceria ar/uatica). Very numerous incon5])icuou5 

 flowers, of minute size, and deroid of colniured enrelopes. 



Photit^raph h'j B. Welch. 



The excessive consumption of pollen, however, might 

 readily prove a source of injui-y which would more than 

 balance the gain derived from the insect-trafiic. It be- 

 came, necessary, therefore, to provide a counter-attraction, 

 which would induce the insects to continue and to 

 multiply their visits, without the destniction of so much 

 pollen. Sugar, in the shape of honey, w-as selected as a 

 convenient and attractive offering to the insects, and in 

 a large number of insect^visit<?d flowers organs were de- 

 veloped whose special function was the providing of houev 

 for the visitors. Thus equipped with a tempting stock- 

 in-trade, the next duty was to advertise it. In this con- 

 nection is it that flowers have undergone their most 

 striking transformations. The in.sects' senses both of 

 sigiit and smell were appealed to. The outer whorls 

 of the flower, whose functions had been formerly chiefly 



prot<>ctive, were enlarged and coloured, till they became 

 highly conspicuous ; and scent was produced, of various 

 sorts, according to the kind of insect visitor which it was 

 intended to attract : and by degrees a very high degree 

 of specialization has been attained. Let us take a few 

 instances. In otu- common Buttercups the outermost 

 whorl of flower-leaves, or culyi. is gi-een, not very large, 

 tough, and hairy. It safely encloses the whole blossom 

 tiU the latter is ready to burst open, keeps it warm and 

 dry, and provides a defensive armoui" against nibbling 

 insects. When the blossom expands, the calvx in some 

 species falls off, its duty completed ; in other species it 

 remains. The next whorl, or cnrolhi. is composed of 

 brilliant yellow petals of considerable size and wondei"ful 

 lustre, which render the flower in the highest degree con- 

 spicuous. These petals have a protective as well as an 

 attractive function, for at night, or in i-aiuy weather, 

 they close like a hood over the inner essential portions 

 of the flower, and protect them from cold and wet. 

 opening again as soon as sunlight comes, and insects are 

 on the wing. The numerous poUen-bearing organs, or 

 stamens, are arranged in a ring inside the corolla, and 

 in their turn surround the female organs, which, in the 

 form of numerous separate carjie?x. are set on a kind of 

 cushion in the centre of the flower. An insect visiting 

 such a flower alights inside the cup-shaped corolla, and 

 as it turns' about in search for honey (which is 

 secreted near the base of the petals and stamens) it rubs 

 the under-stu-face of its bodv against the upper receptive 

 portion of the carpels, depositing thereon some of the 

 pollen which it has presumably picked up in visiting 

 another flower previously, at the same time dusting 

 itself with the pollen of the flower which it is now 

 engaged in plundering. This general description will 

 apply with slight modifications to a large number of our 

 wild-flowers and their mode of fertilization — for instance, 

 to our Stitchwoits. and Wild Roses, and St. Johns- 

 worts, and the manv Umbelliferous plants, but it will be 

 seen that even in these flowers there is a considerable 

 waste of pollen and honev. Both lie open to all comers. 

 The honev mav be stolen bv small insects which do not 

 fly from flower to flower, but have crawled up the stem, 

 or by others whose minute size allows them to get at the 

 honey without disturbing or touching the anthers or 

 stigmas. And. again, both pollen and honey lie exposed 

 to the weather. In irregular flowers, such as the Peas 

 and Vetches. Snapdragons. Deadnettles. and Orchids, 

 we find a much more specialized flower-strticttire. The 

 fiowers. instead of being cup-shaped, with their entrance 

 vertical, are of various peculiar shapes, and have their 

 entrances hoiizontal. Examine the blossom of the 

 common Gorse. One large showv petal extends hori- 

 zontally across the top of the flower, forming a protective 

 roof. Two smaller ones stand vertically one on each side 

 below this. The remaining two petals form the bottom of 

 the flower, iiiid are joined by their lower edge so as to 

 form a boat-shaped structure. The gioup of long ciu-\e(I 

 stamens and pistil lie along the bottom of this keeL 

 The pollen is shed, in part at least, before the 

 flower attains maturity, and falls into the bottom of 

 the keel. A suitable insect, say a bee, visiting the 

 flower, is bound, owing to its peculiar shape, to alight 

 on thekeel. Its weight, by depressing the keel, causes 

 the tip of the stigma to slide out beyond the end of the 

 keel, pushing before it some of the fallen pollen, and 

 both come in contact with the tinder side of the bee s 

 body. It is clear how much more certain and economical 

 this device is than the lavish scattering of pollen carried 

 on by the Buttercup. And here we notice a discrimina- 



