COMPOSITAE 



66i 



478. Cnicus L. 



Style of the hermaphrodite florets very similar to that of Centaurea (montana). 



1565. C. benedictus L. (Hildebrand, 'U. d. Geschlechtsverhalt. b. d. Com- 

 positen,' pp. 57-8, Taf. V, Fig. 31.) — Although the anthers appear normal in this 

 species, the first florets produce no pollen. The neuter ray-florets are so small as to 

 be hardly visible beside the disk-florets. 



479. Centaurea L. 



Ray-florets neuter, tubular, radiating. Disk-florets hermaphrodite. Filaments 

 very irritable. Below the short broad stylar branches a ring of sweeping-hairs 

 directed obliquely upwards ; above 

 this short hairs on the style ; stig- 

 matic papillae on the inner sur- 

 faces of the branches. Kemer 

 states that the pollen is concealed 

 in the anther-cylinder until insects 

 visit the florets, being thus pro- 

 tected from rain and dew. When 

 the proboscis of a nectar-seeking 

 insect stimulates the filaments, they 

 contract so that the crumbling 

 pollen is carried off by the visitor 

 as soon as it is swept out. After 

 removal of the pollen, only cross- 

 fertilization is possible for a short 

 time ; the stylar branches then 

 roll back in such a way that the 

 stigmatic papillae touch the pollen 

 still clinging to the sweeping-hairs, 

 thus effecting self-pollination. I 

 have not myself observed this 

 rolling back of the branches. In 

 some species — C. aipina (Wett- 

 stein) ; C. montana, in the Apen- 

 nines (Delpino), but not at Vienna 

 (Wettstein) — nectar is secreted by 

 the involucral bracts of the bud, 

 as in Serratula lycopifolia, S. cen- 

 iauroides,andJurineamollis. Wett- 

 stein observed the ant Campo- 

 notus sylvaticus Oliv., var. aethiops Latz., on C. aipina in Istria, 



1566. C. Jacea L. (Herm. Muller, ' Fertilisation,' pp. 346-9, ' Weit. Beob.,' 

 Ill, pp. 79-80, ' Alpenblumen,' p. 415; Loew, 'Bliitenbiol. Floristik,' pp. 390, 393, 

 397 ; MacLeod, Bot. Jaarb. Dodonaea, Ghent, v, 1893, pp. 401-2 ; Knuth, 'Bluten- 

 biol. Herbstbeob.,' ' Bloemenbiol. Bijdragen.')— This species is trioecious, ~" 



Fig. 207. Centaurea CyanuSy L. (after J. MacLeod), 

 (i) Disk-floret in the first (male) stage: the style is still con- 

 cealed in the anther-cylinder Kcba) borne upon the filaments (A) : 

 ab is the uppermost part of the cylinder formed by the appen- 

 dages of the anthers. (2) Uppermost part (ai) of (i) in 

 longitudinal section : the two stylar branches are still apposed ; 

 at their base is a ring of hairs, above which is the pollen. 

 (3) Style in the second stage, with diverging branches ; the ring 

 of hairs is laden with pollen-grains, a few of which adhere to 

 the papillose inner surfaces of the branches. (4) Disk-floret 

 in the second (female) stage, half schematic ; the style protrudes 

 from the tip of the anther-cylinder. a5, appendages of the 

 anthers ; Ac, anthers; de, corolla-tube (the nectary (not figured) is 

 situated at «) ; h, filaments ; k, lobes of the corolla ; «, style ; 

 a/A, ring of sweeping-hairs. 



The 



