100 JOURNAL OF THE EOYAL HORTICULTURAL SOCIETY. 



in humanly invented contrivances, by means of which the plant surmounts 

 difficulties brought about by the automatic response itself. Thus, the 

 stimulus of insects appears to enhance the development of the corolla, so 

 that regularly visited flowers are mostly very conspicuous. With this 

 organ the stamens are closely correlated, petals having been originally, 

 but metaphorically, " made out of stamens " ; so that a very general result 

 is that in such flowers they mature their pollen before the stigmas of the 

 same flower are ready to receive it. Hence a difficulty arises in the flower 

 fertilising itself, which places it at a disadvantage, for it not infrequently 

 happens that a flower has become so closely "fitted " to one or few insects 

 that it can set no seed without them. There are two ways by which 

 flowers have overcome this difficulty. If abandoned by insects, they 

 resort to self-fertilisation by modifications of the floral structures, securing 

 a simultaneity in the maturation of the pollen and stigmas, or by the bud 

 remaining unopened and cleistogamous. 



But with conspicuous, strongly " protandrous " flowers, the method 

 adopted, so to say, by nature is to secure intercrossing if self-pollination 

 — the safer process — fails. 



To do this, curious special adaptations are resorted to. As an example, 

 I will first take Salvia, of the Labiate family. Like all irregular flowers, 

 this is descended from a regular pentamerous flower. Eeversions not 

 infrequently occur revealing their ancestral origin. It is worth while 

 enumerating all the points of the existing flower now in perfect adaptation 

 to an insect. (Fig. 18.) 



The calyx is in one piece to support the slender tube of the corolla and 

 weight of the insect. It is nearly bilobed, due to an apparent stretching 

 forwards. Nine additional ribs are run up the calyx to meet the strain in 

 front and sides. 



The anterior petal of the corolla is greatly enlarged to form a landing 

 place, and the conspicuousness of the flower much enhanced. Hypertrophy 

 having affected the anterior side, the two front stamens are greatly increased 

 in size, while the three posterior are atrophied. The two stamens are pushed 

 over to the posterior side, being extraordinarily modified for a well-defined 

 purpose. The filaments are very short, but the "connective," which 

 unites the two anther- cells, is converted into a long curved rod ; the upper 

 anther-cell bears pollen, but the lower has none. The whole swings on 

 a pivot — the point of attachment to the filament — and forms a lever 

 standing in a vertical plane. The short arm is below, the long one above. 

 The style carries two stigmas, and curving forwards presents their surfaces 

 to the front. A bee on entering thrusts its head downwards, striking the 

 two abortive anther-cells, thereby forcing the short arm of the lever down- 

 wards and backwards ; the long curved arm of the lever now comes down in 

 front and strikes the bee on the thorax, thereby depositing pollen upon it. 

 On entering another flower the forked stigmas strike the bee where the 

 pollen has been deposited previously. It is by this mechanical contrivance 

 that the Salvia has overcome the difficulty of never setting its own seed, 

 by transferring the pollen from one flower to another. 



The significant fact to notice in all this lies in the accumulation of 

 coincidences in the structure of calyx, corolla, stamens, and pistil, all 

 conspiring to secure one and the same "end " or cross-pollination, where 



