350 AUTOGAMY. 



flowers are adapted to cross-fertilization. The stamens lie one upon another like the 

 tiles of a roof, and together form a short tube at the bottom of which are a number 

 of closely-clustered carpels, whilst at the free edge of the tube the anthers expose 

 their store of pollen. The first anthers to open are those pertaining to the outer- 

 most and longest stamens, the next belong to those of median length, and the last 

 to the shortest, which are in the immediate vicinity of the carpels. The pollen of 

 the outermost anthers serves mainly for cross-fertilization, and can hardly ever be 

 used for autogamy on account of its position; but even in the case of the latest 

 anthers belonging to the shortest stamens, no pollen could reach the stigmas were 

 it not for the elongation of the carpels, which occurs during the last two days of the 

 flower's duration. The anthers still contain pollen at this late period, and a quantity 

 adheres, besides, to the silky hairs clothing their filaments, so that the slightly 

 divergent stigmas get covered with an abundant supply of pollen as the carpels 

 lengthen and push them up through the pollen-coated tube (see fig. 246 ^ p. 174). 



The flowers of the Lady's Mantle {Alchemilla vulgaris) are likewise protogynous. 

 When a flower opens, the anthers of the four shoz-t stamens are still closed, whilst 

 the stigma is already mature, and is seen in the middle of the flower projecting 

 through and slightly above a kind of diaphragm which is stretched across the floral 

 interior and secretes honey. At this stage cross-fertilization alone is possible; but 

 in the coui-se of twenty-four hours the style grows in an oblique direction, until its 

 extremity bearing the stigma strikes against one of the four anthers, which have 

 meanwhile undergone transverse dehiscence; it thus receives a sprinkling of pollen 

 (see fig. 226^, p. 125). The pollen of the three other anthers is still available for 

 transference by flies to the stigmas of other flowers. 



The above are a few instances of the metliods in which autogamy is effected by 

 elongation of the style or of the entire pistil. Taken generally this process must 

 be classed among the rarer forms of the phenomenon, though it is surprising that 

 it should be so considering the frequency of autogamy by means of the elongation 

 of stamens. The accomplishment of autogamy through the inclination of a style 

 otherwise straight is of even less usual occurrence. The most striking example of 

 this i^rocess is afforded by the bilabiate flowers of the North American Collinsonia \ 

 Canadensis. In the newly-opened blossom the long style stands midway between 

 two exserted stamens which are almost as long as the st}de. Towards the end of 

 the flower's period of blossom, the style begins to slope towards one of the stamens, 

 moving like the hand of a clock through an angle of from 20° to 40° until its stigma 

 comes against the pollen-covered anther borne by the stamen in question. 



A much more common method of bringing about autogamy is for parts of the 

 pistil — usually the stjde — to bend so as either to bring the stigmas into direct 

 contact with the anthers belonging to the same flowei-, or to place them in such a 

 position beneath the anthers as to ensure their catching anj^ pollen tliat may fall 

 out of the loculi. The direction of the style's inflection depends upon the form and 

 mode of insertion of the flower, and more particularly on the position assumed by 

 the anthers. The flowers of the Great Mullein (Verbascum Thapsus), of the Corn- 



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