II COMPOSITE 251 



Each flower-head consists of 200-300 florets. The list 

 of insect visitors is a long one, extending to considerably 

 over 100 species. The pollen presents several crystalline 

 forms in the same anther. Self- fertilisation, in the 

 absence of insect visits, is ensured by the same means 

 as described under Centaurea. In the last stage of the 

 flower the stigmas bend over among the collecting hairs 

 at the end of the style. This is one of the plants in 

 which the structure of leaves grown in the sun difi"ers 

 considerably from those in shade. Fig. 156 represents a 

 section of a leaf grown in shade, Fig. 157 represents a 

 section of a leaf grown in diffused light, Fig. 158 a 

 corresponding section of a leaf grown in sunshine. The 

 last is the thickest, and has two rows of palisade cells in 

 the upper part. 



Crepis 



The pappus is very white. We have six British 

 species, all with yellow flowers. Two have slender beaks 

 to the achenes: in one, C. taraxacifolia, all the achenes 

 have a long slender beak ; in the other, C fcetida, the 

 achenes of the outer row are only short-beaked. Of the 

 other four, two have the lower leaves pinnatifid ; one, 

 C. virens, with the outer bracts of the involucre narrow 

 linear, while in the other, C. biennis, they are oblong 

 linear, with a whitish edge. The last two have mostly 

 oblong leaves, coarsely toothed or entire ; one, C. palu- 

 dosa, with about 10, the other, C. hieracioides, with 

 about 20 ribs to the achenes. 



C. virens is a nearly glabrous annual, while 



0. biennis — as the name implies, a biennial — is more 

 or less hispid. 



C. fcetida is also hairy. The interior of the bracts of 

 the involucre bears appressed hairs. 



C. paludosa — growing in damp places — is, as we 

 might expect, glabrous. The access of creeping insects 

 to the flowers is prevented by glandular hairs on the 

 bracts of the involucre. 



0. hieracioides is glabrous or slightly hairy. 



