378 



HUTCHINSON'S POPULAR BOTANY 



clearly indicated in what was said concerning the elongation of the corolla- 

 tube in Myosotis versicolor ; nor is this the only means by which autogamy 

 is effected by the corolla. In gamopetalous flowers, like the Foxglove 

 (Digitalis], the end may be gained by the loosening and falling of the 

 corolla, the adherent stamens brushing against the stigma as the corolla 

 slips along the style, while in flowers with free petals the very closing 

 of the corolla may ensure self-pollination. An excellent illustration of 

 this last method is afforded by the Devil's Fig (Argemone mexicana), whose 

 handsome yellow flowers bloom only for a single day. Kerner remarks 

 that " in the morning, as soon as the petals are wide open and the tension 



of the sheath of 

 stamens surround- 

 ing the pistil is 

 somewhat relaxed, 

 there is an imme- 

 diate fall of pollen 

 on the concave sur- 

 faces of the petals. 

 . . . When the 

 evening comes the 

 petals close up over 

 the pistil, and one 

 of them brings its 

 inner surface, 

 which is covered 

 with pollen, into 

 direct contact with 

 the stigma." Apro- 

 pos of this subject, 

 it has been ob- 

 served of the 

 Water- crowfoot 

 (Ranunculus aqua- 

 thai when the stream in which it is found is much swollen after 

 rain, the flowers remain submerged and fertilize themselves without opening. 

 In the beautiful Climbing Cobsea (Cobcea scandens) we see how autogamy 

 may be effected by a co-operation of movements. On the expansion of the 

 bud, insect-pollination is the first object provided for, and while the cam- 

 panulate corolla nods invitingly on its stem, the anthers, which are borne on 

 long filaments with hairy bases, lie right in the mouth of the bell, just where 

 the first humble-bee visitor will be sure to knock against them (fig. 458). 

 During this stage the style remains out of sight, with its three-forked stigma 

 tightly closed. In the second stage, anthers and stigma change places, and 

 the filaments of the former, lengthening considerably, twist themselves up 



FIG. 466. PURPLE LOOSESTRIFE (Lythrum salicaria). 



Illustrating the trimorphism of these flowers. The calyx and corolla have 

 been removed. 



