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AMERICAN HOMES AND GARDENS 



June, 1907 



7 — Nasturtium Visited by Hawk Moth 



will not allow us to discuss the remarkable modifications 

 which are exhibited by highly specialized flowers when they 

 are compared with those of a more simple type. We must 

 just, as it were, take the flowers for granted and as we find 

 them, and concentrate our attention upon their mechanical 

 working in relation to their insect visitors. 



To begin, then, with the pea. We see that a pea blossom 

 about to be visited by a bee has a large standard petal as a 

 background and four pinched-up petals below, which act as 

 a kind of platform on which the insect is to alight. But 

 this platform, or stage, has a curious mechanism beneath it. 

 I'his consists in a kind of pocket, formed from two cohering 

 petals, in which are the stamens and pistil of the flower. 

 Into this pocket, which has only one tiny hole at the tip, 

 the moist, sticky pollen is shed by the anthers. Here it lies 

 secure from robber insects until a bee of honest intentions 

 comes to gather honey. As soon, however, as the insect 

 settles upon the platform of the flower, the piston mechan- 

 ism comes into play. His weight depresses the petals; but 

 the style or pistil, being rigid, does not yield to the pressure, 

 and is therefore forced through the small hole at the tip 

 of the pollen-pocket, discharging a quantity of pollen on to 

 the bee's breast. The insect now proceeds to rifle the flower's 

 store of honey. But it has already been converted into a car- 

 rier of pollen, which it will bear away to the next pea flower it 

 visits. The common sage of our gardens has a wonderful, 

 though somewhat minute, contrivance which may be termed 

 the "percussive mechanism," because it works in much the 

 same manner as the trigger of a gun. A reference to the 

 annexed diagrams (Fig. 4) will enable the reader to appre- 

 ciate this fact. The flower's store of honey is, of course, 



8 — Diagrams Showing the Mechanism of the Common Spotted Orchid 



deep down in the tube of the corolla. The visiting bee, in 

 his struggles to reach the sweets with his long tongue, brings 

 his head into contact with two little knobs. As soon as this 

 happens, the two stamens — which are hinged and poised in 

 a very remarkable way — swing over, bearing the pollen- 

 bearing anther-lobes down upon the bee's back and deposit- 

 ing thereon a quantity of their golden dust. Thus the bee 

 is converted into a pollen bearer. 



It now remains to be explained how this pollen is trans- 

 ferred to the pistil of another bloom. The above description 

 refers to the visit of a bee to a newly opened sage-flower, 

 when the stamens alone are fully developed, the pistil being 

 packed away in the hood of the bloom. Later, the pistil 

 grows and curves over, bringing Its forked tip into such a 

 position that the back of a visiting bee is certain to touch It. 

 This Is known as the "female stage" of the flower; and if 

 a bee comes to it from a blossom in the earlier "male stage" 

 It is obvious that cross-fertilization must take place. 



The well known snap-dragon is an interesting type of 

 flowers which possess a contrivance for repelling undesirable 



9 — Wild Arum. Three Flowers Dissected to Show the 

 Three Chief Stages 



Insect visitors. Lord Avebury has called it "a strong box 

 of which the humble bee only has the key." In order to 

 reserve itself for the humble bees, the snap-dragon has made 

 itself into a strong box. The lower Hp of the flower 

 presses closely against the upper — so closely, indeed, that 

 all smaller insect visitors find themselves quite unable to 

 force an entrance. But the big humble bee, with superior 

 strength, readily forces its head and shoulders between the 

 "bull dog" jaws, gathers the nectar, and flies away with the 

 yellow pollen dust upon him to effect the cross-fertilization 

 of the next snap-dragon he visits. 



The problem of shutting out undesirable visitors is solved 

 by many other flowers In another interesting way. They keep 

 their store of nectar either at the extremity of a long, nar- 

 row tube, or of a spur. The passage is ofttimes so narrow 

 that it is quite impossible for even minute insects to crawl 

 down and rifle the sweets; they can alone be reached by such 

 Insects as possess long tongues, or trunks. As an instance 

 of the above we may take first the honeysuckle. Despite pop- 

 ular conviction to the contrary, these sweet-scented flowers 

 are not for the bees, but are adapted for fertilization exclu- 

 sively by long-tongued crepuscular or night-flying moths. 

 The flowers bloom chiefly during May and June — at the 

 very season, that is to say, when hawk moths are abundant. 

 The moths pay their visits on the wing, insert their long 

 tongues into the tubes, and incidentally brush away pollen 



