ly 



AUTOGAMY BY A CO-OPERATION OF MOVEMENTS. 387 



the proboscis is withdrawn, but it does not even then come upon the receptive 

 surface of the stigma. As regai'ds the pollen which, thoug-h shaken out, is not 

 carried away by the insect, but left lying underneath the cone of anthers in the 

 trough of the spurred petal, it also does not reach the stigmatic tissue during the 

 first stage of the flower's development, for the groove is still closed by the project- 

 ing lobe of the stigma. Towards the end of the flower's duration, however, the case 

 is veiy different. The Violas of the Melanium tribe may be x-epresented by the 

 Field Pansy (Viola arvensis), it being the most widely-distributed species of the 

 section. In these plants the cone of cohei-ent anthers gradually breaks up of itself, 

 and the pollen falls out, and fills the hinder part of the channel of the spurred 

 petal. At the same time the lamina of this petal bends in such a manner that 

 its trough is no longer closed by the stigmatic lobe, and the pollen is free to slip 

 towards the mouth of the flower. The only condition now requisite is some change 

 capable of setting the pollen in motion, and this is aftbrded by an inflection of the 

 flower-stalk. Although the flower-stalk in the Field Pansy, Heart's-ease (V. tri- 

 color), and other species of the Melanium tribe undergoes sharp inflection (see 

 vol. i. p. 531) on clear nights, this movement has no influence in promoting auto- 

 gamy at the time when the flower is in full bloom. At the last, however, it causes 

 the mealy pollen to slip further and further down the groove in the lowest petal 

 until it reaches the receptive stigmatic tissue. 



There is a remarkable resemblance between this process and that observed to 

 take place in those Gentians which are called by Descriptive Botanists "acaulescent" 

 or stemless species (Gentiana acaulis, G. angustifolia, G. Clusii, see fig. 312). The 

 flowers of these Gentians are of the type of "revolver-flowers" (cf. p. 250). The fila- 

 ments are adnate to the lower part of the funnel-shaped corolla, and project in the form 

 of five stout ridges towards the ovary, which appears as a column standing up in the 

 middle of the flower; the ridges and the ovarian column, coming into contact with one 

 another, divide the corolla into five tubular passages leading to the honey which is 

 secreted abundantly at the bottom. The anthers are a little higher than half-way 

 up the funnel of the corolla, and are connate into a tube which surrounds the style. 

 Each anther dehisces extrorsely by two longitudinal slits, and immediately after the 

 flower opens the anther-tube is covered all over with pollen. Above the tube is the 

 stigma, which is composed of two notched and lacerated white lobes. The positions 

 of the stigmas and anthers, respectively, ensure cross -pollination through the 

 instrumentality of the humble-bees which fly from flower to flower. If, howevei", 

 unfavourable weather prevails, and the bees stop away, the pollen gradually falls 

 from the anthers as they shrivel, and is transferred to the stigmas in the same 

 flower through the agency of the corolla and pedicel in the following manner. As 

 long as the flower remains upright or ascends obliquel^y (see figs. 312 ^ and 312^) 

 the pollen falling from the shrinking anthers collects above the bases of the fila- 

 ments, where they coalesce with the corolla, and when the corolla folds up for 

 the night or to protect the pollen from rain, the pollen falls down between the 

 folds, which, starting from close to the bases of the filaments, extend nearly to the 



