642 



ANGIOSPERMAE—DICOTYLEDONES 



This species is gynodioecious. Hermann Mfiller states that there are more 

 than 100 hlac-coloured florets in the hermaphrodite heads. The corolla-tubes 

 are 8-12 mm. long, passing into bells 1-1-5 ™™- deep, with 5 linear slightly 

 spreading lobes 4-5 mm. in length. Below, next the involucre, the head is 

 scarcely 8 mm. in diameter, but above, where the corolla-lobes diverge, it is 

 20 mm. or more. As the plant usually bears numerous heads, it is very 

 conspicuous, and the number of insect-visits is considerable. Visitors are the 

 more numerous owing to the fact that the nectar rises as high as the bell of 

 the corolla, so as to be accessible even to insects with a very short proboscis. 

 The stylar branches are almost 2 mm. in length, and remain apposed even 



Fig. 205. Cirsium arvense. Scop, (after Herm. Miiller). (i) Floret in the 6rst (male) stage. 

 (3) Pollen-grain in surface view (x 400). (3) Do. in optical section. (4) Floret in the second (female) 

 stage : pollen still clinging to the style. (5) Uppermost part of the style ( X 88). a, anther-cyhnder ; 



by long sweeping-hairs ; c, short do. ; d, stigmatic papillae ; r, pollen. 



during the second stage of anthesis, only their margins, which are beset with stig- 

 matic papillae, protruding. In the first stage a large quantity of pollen is swept Out 

 of the anther-cylinders. The sticky pollen-grains are beset with pointed out- 

 growths, and readily adhere to the hairy under-sides of insects creeping over the 

 inflorescence : in favourable weather they are soon brushed away by visitors, so 

 that crossing is assured. But if insects do not pay their -visits till after the stigmatic 

 papillae protrude, self-pollination may also occur. If such visits entirely fail, 

 self-pollination may also be automatically effected by the fall of poOen-grains from 

 the sweeping-hairs upon the stigmas. MacLeod states that the species is gyno- 

 dioecious on the Blankenberg dunes, and Warnstorf says this is also the case at 



