AUTOGAMY BY THE CLOSING OF THE PERIANTH. 373 



of torsion takes place which brings the folds into the position shown in transverse 

 section in fig. 305 *. The re-entrant angles come into direct contact with the 

 surface of the anther- tube (see figs. 305^ and 305^) and take from it some of the 

 pollen, which is very adhesive. On the next day, and on the third and fourth days, 

 the flower opens and shuts again. During that time almost every part of the 

 flower grows in length; the filaments gain 1 mm., the pistil 3 mm., and the inferior 

 half of the corolla as much as 5 mm. In consequence of this growth the pollen 

 transferred to the folds of the corolla from the anther-tube is raised 5 mm., and 

 rests at the same level as the stigmas, which have in the meantime become diver- 

 gent. When darkness sets in, and the corolla once more falls into folds and closes 

 up, the pollen affixed to the re-entrant angles is transferred to the stigmatic tissue. 

 The process is greatly facilitated by the fact that, at this final stage of flowering, 

 the internal folds assume a somewhat different form and position (see fig. 305 ® ) 

 for in consequence of this change the parts besmeared with pollen are brought still 

 nearer to the middle of the flower. This marvellous contrivance for promoting 

 autogamy may also be observed in Gentiana Pneumonanthe, a species which grows 

 in damp meadows in England and all over the continent of Europe, and in this 

 instance the elongation of this funnel-shaped portion of the corolla in the interval 

 between the first and last occasions of the flower's closing amounts to some 7 mm. 



The phenomenon occurs in a much simpler form in Sternbergia and Colchicum, 

 belonging to the orders Amaryllidaceae and Liliacese respectively. The flower of 

 Sternbergia lutea has an erect funnel-shaped perianth composed of six segments, 

 three of which are rather longer than the other three. The six upright stamens 

 have nectar secreted at their bases, and are adnate to the segments of the 

 perianth; they are arranged in two whorls round the styles, and have their 

 anthers turned outwards. The styles rise up in the middle of the flower in the 

 form of three long threads. The stigmas, in w^hich the styles terminate, are higher 

 than the anthers throughout the period of bloom, and as, after the dehiscence of 

 the anthers, the pollen adheres to the internal walls of the loculi, it is not spon- 

 taneously transferred to the stigmas in the same flower. The flowers are protogy- 

 nous, and at the commencement of their bloom are adapted to cross -pollination 

 through the agency of insects. Even after the extrorse anthers have dehisced, 

 insects entering the blossom in quest of honey brush first against the stigmas, 

 and only subsequently come into contact with the anthers resting at a lower level. 

 The perianth is open in the daytime alone; in the evening its segments close 

 together so tightly that their inner surfaces touch the extrorse anthers and become 

 smeared with pollen. This happens the very first evening following on the dehis- 

 cence of the anthers. The pollen affixed to the perianth-segments does not reach 

 I the level of the stigmas till the following day. Its ascent is due to an elongation of 

 i the lower regions of the perianth-segments. There is a simultaneous growth of the 

 j other parts of the flower, but it is surpassed by the extraordinary increase in the 

 i length of the perianth-leaves. Whilst the styles grow 4 mm., and the stamen- 

 filaments from 9 to 10 mm., these segments grow 18-5 mm. Afterwards, when the 



