. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. 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
. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. 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
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