AUTOGAMY BY THE FALLING OF THE COROLLA. 367 



known at present in which the stigma after heing at first, rather higher than the 

 anther-, is overtaken by them and besmeared with pollen owing to an elongation of 

 the calyx and consequent raising of the stamens, which are adnate to (lie tuhe of 

 the calyx. 



In many plants autogamy depends upon the fact that as the corolla falls off, its 

 tube slips over the stigma, so that the latter rubs against the anthers, which are 

 still laden with pollen, or against the inside of the corolla, which is also besmeared 

 with that substance. This process presupposes that when the flower is in full 

 bloom the anthers are overtopped by the stigma, and that the latter is still in a 

 receptive condition at the time the corolla becomes detached and drops. Both these 

 conditions are as a fact fulfilled in all plants of this category. In the species of the 

 genus Gilea (Polemoniaceae), and in the Brazilian plant Psychotria leucocephala 

 (Rubiacese), the long filiform styles branch into divergent arms, which bear the 

 delicate stigmatie tissue: and at the period of full bloom, these style-arms project 

 far above both the limb of the corolla and the anthers. Consequently, insects 

 alighting on these flowers encounter first of all the stigmas, and if they are laden 

 with foreign pollen they occasion cross-fertilization. There is, on the other hand, 

 in this form and position of the stigmas the further advantage, that, in case of a 

 dearth of insect-visitors, the stigma may still acquire a supply of pollen when the 

 c< »n ilia falls oft' — that is, at the very last moment of flowering. It is not unusual in 

 these plants to see the corolla, after it has become detached, hanging for quite a 

 long time from the long style and divergent stigmas, and this delay in the process of 

 severance must materially assist the accomplishment of autogamy. The detached 

 corolla persists in a similar manner in flowers with capitate, or short-lobed stigmas, 

 as, for instance, in Rhododendron hirsutum, in Digitalis, Anchusa, Cestrum, and 

 various other Scrophulariaceaj, Boraginacese, and Solanaceae. In the case of Rhodo- 

 dendron hirsutum, as the corolla slips along the style, the stigma brushes off the 

 pollen, which has invariably been discharged from the anthers before the flower 

 opens and been caught upon the hairs in the interior of the corolla-tube. In 

 Cestrum aurantiacum, the anthers, which are borne upon stiff and slightly -inflexed 

 filaments, are pressed against the style, and the corolla is left hanging from the 

 style, usual ly for a couple of days after its detachment, and does not fall till after 

 fertilization has taken place, when the style also drops off. A great variety of con- 

 trivances exists with the object of promoting this method of autogamy by means of 

 a falling corolla. A brief account of three of them will now be given. The flower 

 of the Moth Mullein ( Virbascum Blattaria), which may be taken as the type of a 

 large number of flowers of Scrophulariacese, has a corolla with a very short tube 

 and the limb spread out at right angles to it (rotate). Adnate to the tube are five 

 stamens clothed with woolly hairs of a violet colour. The three upper stamens are 

 a little shorter than the two lower ones, and all of them project obliquely beyond 

 the limb of the corolla. The central style is still further exserted, and serves as a 

 perch for insects to alight upon. It is obvious that so long as the parts of the 

 flower are disposed in this manner every insect which arrives with a supply cf 



