AUTOGAMY BY SHORTENING OF PISTIL. 347 



gently away from the veh^ety stigma at 9 a.m., i.e. shortly after the expansion of 

 the petals, whilst three or fours hours later, when the petals close up again, they 

 undergo spiral inflection from right to left and lay their anthers upon the stigmas. 



The cases in which the stigmas are the agents in the operation of transfer to 

 themselves of pollen from the anthers of the same flower may be classed in two 

 divisions, (1) those in which a direct contact between the stigma and the anthers is 

 effected by some definite bending or other movement of particular parts of the 

 pistil; and (2) those in which the pollen is first deposited by the anthers and stored 

 in some part of the flower other than the stigma ; ultimately the stigmatic tissue is 

 brought in contact with it in the same manner as in (1), i.e. by some movement on 

 the part of the pistil. 



The cases comprised in the first division fall naturally into four groups. 



To the first group belong all those in which autogamy is produced by contraction 

 of the style. The Cactiform plants of the Mexican plateaux, in particular, various 

 species of the genera Cereus, Echinopsis, and MamTnillaria, exhibit in their flowers a 

 number of filiform stamens, arranged in a close spiral around the passage leading to 

 the honey secreted on the floral receptacle. In the midst of this thicket of stamens 

 stands a long style which terminates in a stellate stigma. The anthers are already 

 covered with pollen when the petals unfold, but the stigma, which jDrojects consider- 

 ably beyond the anthers, is still closed, its fleshy lobes being coherent and forming 

 a kind of club, so that there can be no possibility of its being dusted with pollen. 

 Thus the flowers are markedly protandrous, and the pollen liberated during the first 

 part of their period of bloom can only be used for cross-fertilization. The next step 

 is the opening of the stigma and spreading out of its lobes into a star in front of the 

 entrance to the nectary. Insects now alighting are obliged to brush against the 

 stigma before thej^ can get at the nectar, and in so doing they deposit a portion of 

 the store of foreign pollen with which they are laden upon the stigma and initiate a 

 process of cross-fertilization. This stage may last a few hours only, or several days, 

 or over a week, according to the species. When the term of the flower's duration is 

 nearly reached the style contracts in length, and the stigma, which has hitherto been 

 above the anthers, is drawn into the midst of them, so that it cannot fail to get 

 covered with the pollen, of which there still remains a quantity clinging to the 

 anthers. In Cereus dasyacanthus the stigma soon after the opening of the flower 

 projects 1 cm. beyond the anthers. The length of the style bearing the stigma is at 

 that time 20 cm. When the flower is nearly over, the style is only 16"5 cm. long, 

 and the stigma is therefore drawn in through a space of 3'5 cm. and no longer 

 surmounts the stamens, but, on the contrary, is 2 5 cm. lower than the anthei'S 

 of the longest stamens. 



The second group includes all cases where autogamy is brought about by an 

 elongation of the ovary or the style. Ephnediimi aljnnum, a native of the warm 

 valleys of the Southern Alps, has four sepals arranged crosswise and beneath these 

 — the flowers being partially inverted as shown in figs. 298^--'^ — four petals 

 fashioned like little slippers and containing an abundance of honey in their blunt 



