APPEND IX^A 



537 



any bracts subtending them. Centrally are the yellow florets of the disc, 

 peripherally the ray-florets. Each disc-floret consists of : 



Calyx, represented only by a rim round the upper limit of the inferior 

 ovary. There is no pappus. 



Corolla, petals 5, gamopetalous, superior. 



Androecium, stamens 5, alternating with the petals, epipetalous, inserted 

 by separate filaments upon the throat of the corolla, but with the anthers 

 united laterally into a tube (syngenesious) . 



Gynoecium, carpels 2, antero-posterior, syncarpous. Ovary inferior, uni- 

 locular, containing a single anatropous ovule. Style elongated, and bearing 

 up through the tube of the anthers the two 

 lobes of the stigma, which diverge beyond it 

 in the later stages of flowering (Fig. 442, vii.) 

 The white ray- floret consists of : 

 Calyx, as before. 



Corolla, petals 5, gamopetalous ; tubular 

 below, elongated above into a narrow strap- 

 shaped ray representing the three anterior 

 petals, the two posterior being here obsolete. 

 Androecium, absent. 

 Gynoecium, as before (Fig. 442, v.). 

 Fruit. Each flower produces a dry achene, 

 which at maturity is shaken out from the 

 protecting involucre. There is no pappus. 



Pollination. The mechanism is here essen- 

 tially the same as in Groundsel, but with 

 addition of the attractive ray -florets. In 

 the first flowering stage the disc-florets offer 

 pollen ; in the second stage the expanded 

 stigmas to the insects that are attracted by 

 the colour and honey (iii. iv.) Any crawling 

 insect will effect crossing. But if this fails 

 self-pollination is also possible 



(44) A third more elaborate type is seen in 

 Cornflower (Centaurea cyanus, or C. montana 

 will serve) . The general structure is the same, 

 but the ovoid head is tightly enclosed by the appressed bracts with brown 

 margins. The receptacle is flat and bristly. The flowers are all tubular, but 

 the outermost are neuter, and coloured, with long tubular two-lipped and 

 5-lobed corolla, and abortive stamens and ovary. The inner florets are 

 hermaphrodite, and of the usual type, with pappus of short unequal bristles. 

 The lower part of the corolla-tube is tubular and narrow, the upper is globose, 

 bearing five distal lobes. The syngenesious anthers form a dark purple tube, 

 with a terminal beak. The style bears below the stigma-lobes a ring of 

 bristles, which acts like a sweep's brush upon the pollen. The flowers are 

 protandrous as before. The filaments are curved and sensitive, contracting on 

 the stimulus of touch. This is received by hairs radiating out from them ; 

 honey is secreted at the base of the corolla (Fig. 443). 



The insect visitors are most commonly bees. Inserting the proboscis into 



FIG. 443. 



Stamens and^style of Centaurea. 

 A, in the unstmiulated, B, in the 

 stimulated state. 1 he style in the latter 

 projects Leyond the anthers, and the 

 pollen has been brushed out. (After 

 Strasburger.) 



