APPENDIX A 637 



fresh insect visit. The effect of such visits will be, first, to rub the stigma, and 

 make it receptive, while as it emerges first from the keel it receives any pollen 

 brought from other flowers by the bee ; second, to deposit a fresh supply of 

 pollen on the insect. A cross-pollination is thus a virtual certainty. 



(31) The flower of the Garden Pea (Pisum sativum), may be taken as an 

 alternative type, the construction being essentially the same as in Lotus, 

 though differing slightly in details of its mechanism. The weight of the visit- 

 ing-insect depresses the interlocking wings and keel as before ; but the latter 

 is closed only along the anterior margin, so that when it is depressed the 

 stirrer stamens and carpel rise out of the boat- like keel, and come in contact 

 with the lower surface of the insect. The style bears a brush of hairs, which, 

 as it rises, sweeps out the pollen on to the insect's body ; but the stigma reaches 

 its body first, and receives thus such pollen as it may have brought. The 

 flower is elastic and recovers, making successive visits possible. The mechan- 

 ism is less precise than in Lotus, but still very effective. It requires a strong 

 insect, and in absence of cross-pollination self-pollination is possible. 



These examples serve to illustrate the exact mechanism of the Papilionace- 

 ous flower, and the way in which slight differences may affect the process of 

 their pollination. 



ORDER; UMBELLALES. 



Family : Umbelliferae. Example : Cow Parsnip. 



(32) The Cow Parsnip (Heracleum Sphondylium, L.) is a coarse perennial 

 herb, with massive storage stock, which sends up the annual leafy and flowering 

 shoot. The stem is hollow and fluted, and bears alternate leaves with broad 

 sheathing base, and irregularly cut lamina. The main inflorescence is terminal, 

 but others may arise in the axils of the upper leaves. It is a compound 

 umbel (p. 262, Fig. 185). The flowers are individually small, but many being 

 grouped together, and all at the same level, the aggregate inflorescence becomes 

 a conspicuous feature. Each flower is borne upon a slender hairy stalk, which 

 widens out just below the flower itself into a flattened green body. This 

 is the inferior ovary, and the flower is epigynous (Fig. 490). Care should be 

 taken to select perfect flowers for observation, as the parts fall away early. 

 The flower consists of : 



Calyx, sepals 5, superior, present as minute teeth visible between the petals. 

 The odd sepal is posterior. 



Corolla, petals 5, polypetalous, free, superior. Each is notched at the free 

 edge. In the marginal flowers the petals are unequal, the outermost being the 

 largest. 



Androecium, stamens 5, free, epigynous, alternating with the petals ; bent 

 inward in bud, but straightening when mature. 



Gynoecium, carpels 2, syncarpous ; stigmas 2, styles widening downwards 

 into two yellowish green nectaries. Ovary inferior, bilocular, with one pendu- 

 lous ovule in each loculus. 



Fruit, a flattened oval body, which matures dry. When ripe it splits into 

 two halves (mericarps), attached at first by a slender middle column/from which 

 they later break away, and are readily carried by the wind. Each mericarp 

 contains a single albuminous seed, and is marked by elongated oil-glands, four 

 on the outer and two on the inner flattened sides* . 



