DEPOSITION OF POLLEN. 281 



have bilabiate stigmas which exhibit sensitive movements. When the pollen is 

 deposited by an insect on the lower lip of the stigma, which stands in its way as 

 it enters (280 *), the two lips immediately close together like the leaves of a book 

 (280 '), and thus the pollen is carried to that part of the stigma where it undergoes 

 further development. When the insect withdraws its proboscis there is no chance 

 of the pollen which it is taking from the anthers getting into the interior of the 

 stigma, since the stigma is still shut up and no longer stands in the way of the 

 insect (280 ^). The stigma of Mimulus luteus remains closed after being stimulated 

 with a needle for about five minutes; when it again opens, the lower lip resuming 

 its former position, it may be again closed if further stimulated. In other species 

 of the genus, as also in Martynia and Catalpa, the same phenomenon is observable. 

 None of the previously-mentioned plants appear to keep their stigmas closed more 

 than two minutes. This repeated opening of the stigma is very important in case 

 the first insect visiting the flower should have brought no pollen with it. Since the 

 stigma opens again it has apparently some expectation of a second visit. Should 

 this also be unsuccessful it may open a third time. The opening and closing 

 usually continue until at length an insect deposits pollen on the stigma. When 

 this happens the stigma, though opening yet again for a brief period, remains per- 

 manently closed so soon as the influence of the pollen is felt. 



The contrivances described above are based on the fact that the pollen stroked 

 oif the visiting insects by the projecting edges, bands, and lobes, is conducted from 

 them to the portion of the stigma adapted to receive it. To this first group of 

 contrivances for retaining pollen may be added another where the insect on 

 entering into the base of the flower leaves the pollen it has brought on the papillose, 

 superficial cells of the stigma. This occurs, for example, in the flowers of 

 Malvaeese and Caryophyllacese, the styles of which are studded with long tube-like 

 papillae; they act like brushes. In the flowers of the Eock-rose (Helianthemum), 

 and in those of the Day-Lily (Heinerocallis), long papillae are grouped paint-brush- 

 wise on the capitate stigma, but most frequently the trimming of very numerous 

 long and crowded papillae has the appearance of velvet, and such stigmas are termed 

 "velvety" by descriptive botanists. The genera JErythrcea, Daphne, and Hibiscus 

 may be mentioned as well-known plants with velvety stigmas. In many plants 

 the stigmatic papillae are but slightly prominent, the surface appearing rough, 

 irregular, or granulated. If the flowers are crowded, and the deposition of pollen 

 occurs simultaneously on numerous stigmas, these are usually linear or only beset 

 with papillae on one side, as in Cephalaria, or clothed all over, as in Armeria, but 

 always so formed and placed that the insect moving over the flower-head may rub 

 off its pollen as easily and quickly as possible on to the stigmas. In those plants 

 where the stigma rising in the middle of an erect, shallow flower is used as a 

 resting-place by the insect, either the whole surface is thickly beset with papillae 

 {e.g. in Roemeria, fig. 279 "), or they are arranged in the form of rows distributed 

 in radial Hues, as in the Poppy (Papaver, fig. 279^^). It frequently happens that 

 the papillae only border the edge of the stigma, resembling eyelashes on an eyelid. 



