THE WELCOME OF THE FLOAVERS 



377 



style, which we have described as taking place in the Groundsel, may be 

 seen to more advantage in the larger florets of most species of the Knap- 

 weed family (Centaurea, fig. 455), as well as 

 in most of the Willow-herbs (Epilobium, 

 fig. 456). Take, for instance, the beautiful 

 Mountain Centaury (Centaur ea montana}. 

 This plant has a very long list of insect 

 visitors, and yet, when need so requires, 

 the florets are quite competent to pollinate 

 themselves. The anthers are united into a 

 tube which conceals the greater part of 

 the style and is itself almost concealed by 

 the corolla-tube. The anthers open to- 

 wards the style, upon which in consequence 

 they shed their pollen (introrse dehiscence), 

 and, as might be expected, a good deal of 

 the precious dust gets scattered on the hairs. 

 Here, unless removed by insect agency, it 

 remains until the florets enter upon their 

 last stage ; when the style-branches roll 

 back, and in so doing bring their stigmatic 

 surface in contact with the pollen on the 

 circlet of hairs. Thus autogamy is effected. 

 To describe even a tithe of the means 

 by which the same important end is brought 

 about in other flowers would require more 

 space than the scope of this work allows. 

 In the case of pendent flowers like Sol- 

 danella, where the style projects beyond 

 the stamens, the pollen may get sprinkled 

 on the stigma : and this may also be the 

 case in upright flowers when the anthers 

 are placed above the stigmatic surface, as 

 in the Lilac (Syringa). We have seen how 

 the lengthening of stamens may bring 

 about autogamy, and instances are not un- 

 common in which the curving or erecting 

 of those organs fulfils the same purpose. 

 The pistil, too, may shorten or elongate, 

 curve or straighten, when self-pollination 

 is the object ; or (as in the case of the 

 Mountain Centaury above described) the 

 stigma itself may be adapted to this end. 

 The important part which the petals sometimes play in this process was 



Photo btj] 



[/?. Step. 



FIG. 465. PURPLE LOOSESTRIFE 



(Lythrum salicaria). 



See also fig. 466. 



