128 



THE FLOWERING PLANT. 



of the way, so to speak. An upper stamen would be so blocked 



up by it as to be of little use. 



Take, for example, foxglove. 

 The lower lip forms a landing- 

 stage from which an insect can 

 creep into the belL Only a large 

 form like the humble-bee is use- 

 ful, as the size of the corolla pre- 

 vents others from touching the 

 stigma and anthers. The flower 

 is to some extent proterandrous, 

 and, as in so many cases, the 

 stigma projects beyond the sta- 

 mens. The didynamous con- 

 dition is well adapted for dis- 

 playing the anther lobes, which 

 are at first transverse, but after- 

 wards move into a vertical posi- 

 tion. 



The personate corollas of toad- 

 flax and snapdragon can only be 

 forced open by bees. In the 

 latter case humble - bees are 

 almost the sole visitors, as others 

 are not strong enough to press 

 down the lower lip. 



Musk is particularly interest- 

 ing among lipped forms, from 

 the fact that the stigma is in 

 the form of two flattened sensi- 

 tive (especially in the large 

 scentless musk) lobes, which 

 close on contact. Pollen can 

 thus be deposited in it by an 

 arriving, but not by a departing 

 guest. 



White dead nettle presents an 

 arrangement common in labiate 

 flowers. The lower lip forms a 

 convenient landing-stage ; the 

 upper one not only protects the 

 stamens and pistil, but keeps 



FIG. 51.— Structure of Pansy [from Sachs]. 

 All but A. magnified. A. longitudinal 

 section of flower. B. ovary and anthers, 

 the former fertilized and swollen ; the 

 filaments have been broken off and the 

 anthers carried forwards by growth of 

 ovary. C. stigma, style, and top of ovary. 

 D. transverse section of ovary. E. trans- 

 verse section of young anther, showing 

 two pollen-sacs in each lobe and con- 

 nective uniting lobes ; v. bracteole ; I, V. 

 sepals; Is. appendage of sepal; c, c, c. 

 petals ; cs. spur of lower petal ; a. anthers ; 

 /. filaments; /*. nectar-excreting appen- 

 dages of lower stamens ; n. stigma ; 0. 

 opening of stigma ; Ip. lip of stigma ; gr. 

 style ; fK. top of ovary ; sp. placentas ; 

 sK. ovules. 



them pressed firmly down. A 

 visitor settling on the lower lip touches first the forked stigma, 

 which hangs down a little, and then the anthers of the didy- 



