372 



AUTOGAMY. 



of the operation consists in an elongation of the corolla. Types of this group are 

 afforded by Gentianaceas of the subdivision Coälanthe (Gentiana asclepiadea, G. 

 Pneumonanthe, &c.), Liliaceae (Colchicum), Aniaryllidacese (Sternhergia), Iridacese 

 of the genus Sisyrinchium, and those Composites whose capitula are furnished with 

 ligulate florets {Crepis, Hieraciiim, Hypochoeris, Leontodon, &c.). 



Gentiana asclepiadea (see fig. 305) is one of the sub-alpine species of the Baltic 

 flora, and has protandrous flowers. The anthers are united into a tube, as in the 

 case of Composites and Bell-flowers. They do not, however, discharge their pollen 

 into the tube, but behave in this respect in the same manner as those of HypecouTii, 

 that is to say, they open by longitudinal fissures down their external faces, so that 

 after dehiscence the outside of the anther-tube is covered all over with pollen 



Fig. 305. — Autogamy effected by means of the corolla. 



1 Gentiana asclepiadea. riover-bud shortly before it opens for the first time. - Open flower in the last stage of development. 

 3 Longitudinal section through a flower which has just opened for the first time. * Transverse section through the same 

 flower. 5 Longitudinal section through a flower closed for the first time. Pollen is affixed to the edges of the folds into- 

 which the corolla is thrown. « Longitudinal section through a flower which has opened for the last time. ' Longitudinal 

 section through a flower which has closed for the last time. The pollen is being transferred from the folds of the corolla 

 to the reflexed stigmas, s Tranverse section through the same flower. The anther-tube in ^, s, s, and " is represented in 

 optical section. 



(see fig. 305^). The linear style-branches bearing the stigmatic tissue are at this 

 stage closely united and as yet immature. Humble-bees are attracted in large 

 numbers by the rich store of honey in the floral interior, and as the funnel-shaped 

 corolla is wide open in the daytime the insects enter, and are often entirely engulfed 

 in the flower. If the visit is paid to a young, newly-opened flower the insect 

 loads itself with pollen by coming into contact with the tube of anthers. Two days 

 later the linear stigmas separate and curve over downwards. Their position now 

 renders it inevitable that they should be touched by the bees, of which a large 

 number continue to visit the flower, there being still plenty of honey in it. If these 

 visitors have recently visited younger flowers they are sure to effect cross-fertiliza- 

 tion. The corolla is disposed in peculiar folds, as is shown in figs. 305 ^ and 305 ^; 

 to describe them suflaciently briefly for our present purpose would not be possible. 

 When the flower expands in the morning these plaits open out ; at sunset they are 

 again drawn in towards the middle of the funnel, and at the same time a movement 



