GRASS, MONKSHOOD 385 



Amongst entomophilous plants, too, we have seen that 

 diclinous and dichogamous species are found ; but if we 

 look over the common flowers in any garden or meadow we 

 see at once that the hermaphrodite condition predominates. 

 In a great many hermaphrodite flowers pollination is nearly 

 as indiscriminate, though carried out by insects, as it would 

 be with wind carriage. This is the case in the floral classes 

 A and PO, and to a less extent B and AB. In such cases, 

 where small insects wander at will over the flower, indirect 

 autogamy must be as frequent as cross-pollination. The 

 situation is altered if the flower is dichogamous. Thus 

 proterandry is common in the saxifrages, Chrysosplenium 

 oppositifolium is proterogynous, and the Umbelliferae are 

 usually proterandrous. In the more highly specialised 

 flowers dichogamy is frequently combined with a relation 

 of the essential organs to each other and to the form of 

 the corolla, which determines how the flower is visited, 

 and is such that cross-poUination is favoured. 



Further Examples of Floral Mechanism. — In the case of 

 Salvia pratensis , already described, we have a good example 

 of a fine floral mechanism combined with proterandry. In 

 the monkshood, Aconitum Napelhis, the posterior sepal 

 forms an arched hood over the stamens and carpels, and, 

 with its brilliant blue colour, is the most showy part of the 

 flower. The other four sepals, like it, resemble petals and 

 are also brightly coloured ; the two lower form a land- 

 ing-stage for the humble bees which alone pollinate the 

 flower. The two narrow petals curve up under the hood 

 and function as nectaries. The bee, entering the newly 

 opened flower, brushes against the upturned stamens and 

 the lower side of its body is dusted with pollen. Later on 

 the stamens wither and curl down, their place being taken 

 by the stigmas, which are now receptive. A bee visiting the 

 flower at this stage covers the stigmas with pollen from 

 another flower. The genus Aconitum is of special interest, 

 because its distribution lies wholly within that of the humble 

 bees, on which it is completely dependent for pollination. 

 The northern limits of the monkshoods and the humble 



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