GLASGOW SOCIETY OP FIELD NATUKALISTS. 113 



The outer coat of the pollen granule is dilated into two large 

 hollow chambers, which are filled with air. This serves to render 

 the pollen easily carried about by the wind from one plant to 

 another. In the pines there is a very large quantity of pollen 

 developed, and it has been stated that, in America, the pollen 

 from the pine forests is sometimes carried to a great distance by the 

 wind and falls like showers of sulphur. 



So much for the first group which shows no special adaptation 

 for the prevention of self-fertilisation. Let us now pass on to 

 the second, and by far the most interesting group, which shows 

 such varied and beautiful adaptation for the prevention of self- 

 fertilisation. 



Let us first take some simple case of protandrous dichogamy as 

 illustrated by the order Malvacecp,. In this order the stamens are 

 united so as to form a tube, in the interior of which the pistils are 

 situated. In the male stage the stamens shed their pollen while 

 the pistils are in the centre ; in the female stage the anthers drop 

 oflF and the pistils appear, and the stigmas separating from each 

 other, curve around till they occupy the same position as the 

 stamens formerly did, so that an insect visiting the flower in the 

 first stage would get dusted over with pollen, and then, on visiting 

 a flpwer in the second stage, would touch the stigmas with the 

 same part of its body as had formerly touched the stamens, and so 

 pollen would be deposited on the stigma and the plant fertilised. 



In Lamium album (White Dead Nettle) we have a bilabiate 

 corolla (Fig. 11). 



The honey is at the bottom of the tube, and is protected from 

 rain by the arched upper lip and by hairs. The lower lip projects 

 considerably, and forms an admirable landing place for insects. 

 The length of the corolla tube and certain hairs in the throat of 

 the corolla prevent the access of small insects, which would remove 

 the source of attraction for bees without efiecting the grand object 

 for which it was designed. The arched upper lip, in its form, size, 

 and position is admirably adapted as a protection against rain, as 

 well as to prevent the anthers and pistil from yielding too easily 

 to the pressure of the insect, and thus to ensure that it should press 

 the pollen which it has brought from other flowers against the 

 pistil. The stamens do not form a ring round the pistil as in the 

 last case. On the contrary, one stamen is absent, while the other 

 four lie along the outer arch of the corolla on either side of the 



Q 



