AUTOGAMY IN SPRINKLING FLOWERS. 333 



eontact with the stigma. The loculi, full of adhesive pollen, face outwards, and are 

 so placed that insects coming in quest of honey must rub off the pollen emerging 

 from their slits. The stigmas, on the other hand, assume such a position that the 

 insects are obliged to touch their receptive tissue before brushing the anthers. 

 Owing to the relative positions of stigmas and anthers cross-pollination is no doubt 

 effected hy insects in a large number of cases, and as only the backs of the anthers 

 I'est upon the stigma autogamy is, for the time, impossible. But tow^ards the close 

 of the flowering period the anthers are twisted round, with the result that the 

 pollen of each loculus touches the stigma. Another circumstance contributory to 

 this autogamy is that during the time of flowering the perianth-tube elongates from 

 5 to 15 mm., and the filaments, which are adnate to the perianth, from 3 to 4 mm. 

 The anthers are in consequence pushed past the stigmatic margins and leave more 

 pollen upon them than would otherwise be the case. 



Convolvulus Siculus, a native of the shores of the Mediterranean, may be taken 

 as a type of several annual Bindweeds wherein the style bifurcates into two narrow 

 filiform branches of considerable length which bear the receptive tissue and represent 

 stigmas. One of these stigmas is erect, and continues the style in a straight line, 

 whilst the other stands away at an angle of 60°, and forms a barrier in front of the 

 approach to the floral receptacle. The stamens are adherent to the style, and at 

 the time that the corolla opens the anthers rest against the erect stigma. At the 

 period of dehiscence the anthers face outwards so that the upright stigma encom- 

 passed by them cannot receive their pollen when the flower first opens. On the 

 other hand, the position of the anthers is favourable to the abstraction of pollen by 

 insects seeking the honey in the interior of the flower. Later on, when the anthers 

 shrivel they become covered all over with pollen, and then it is that a portion of 

 it is transferred to the erect stigma, thus effecting autogamy. The second stigma, 

 which lies across the entrance, seldom has pollen from the anthers of the same 

 flower affixed to it; but pollen conveyed from other flowers is rubbed off insects on 

 to this stigma, so that here we have an instance in which one stigma is adapted to 

 autogam.y and another to cross-pollination. 



The process of autogamy occurs in pendent flowers, the anthers of which are 

 joined together in a central cone, through a relaxation of the filaments towards the 

 close of the flowering period, in consequence of which the loculi full of pollen no 

 longer close together so tightly as before. The mealy pollen falls from the dislocated 

 cone upon the stigma, which is still in a viscid and receptive condition. As types of 

 this category of plants we may take the Snowdrop (Galanthus), Soldanella, of w^hich 

 previous mention has been made (see fig. 278 ^, p. 275), and Dodecatheon, wdiich is 

 allied to Soldanella, but in respect of the form of its flowers resembles Cyclamen. 

 During the first part of their flowering-period they are adapted to cross-fertilization. 

 The style projects far beyond the cone of anthers. Insects in search of honey begin 

 by brushing against the stigma and then for a moment dislocate the anthers, letting 

 a sprinkling of pollen fall on their heads. On visiting other flowers they rub this 

 pollen on to the stigmas and so promote cross-fertilization. If, however, no insect» 



