THE ANGIOSPERMAE 



1349 



while the style lies downwards and outwards from them. Automatic self- 

 pollination is therefore impossible. 



The pollination is simple. The lower petal provides a platform on which 

 the fly settles and in so doing it comes into contact with the style and, if 

 there is pollen on the ventral surface of the insect, pollination is ensured. 

 In its efltort to reach the nectar the insect grasps the filaments of the two 

 stamens, drawing them towards it under its body, and thereby becomes 

 dusted with pollen. The flowers only last one day and then the corolla is 

 shed, together with the two stamens, by slipping over the style. 



iv. Flowers Pollinated by Small Insects 



Miiller was responsible for the suggestion that a separate class of pollina- 

 tion should be made to include those flowers which are visited by tiny 

 insects. These insects belong to various groups, but as far as pollination 

 is concerned there is agreement in the fact that the floral parts are modified 

 so that the anthers will come into contact with their tiny bodies. In most 

 flowers these insects would be of no value, for they would pass around the 

 stamens and style without touching the vital parts. Indeed, as we have seen, 

 many flowers are specially formed to preclude their entry. 



Observations have only been made on a small number of flowers which 

 appear to belong to this group, though further research is likely to prove 

 that more types rely upon these little insects than is recognized at present. 

 The insects concerned include members of the Hymenoptera, Diptera, 

 Coleoptera and possibly the Hemiptera and Thysanoptera as well. 



Fig. 1258. — Herminium monorchis. A, Inflorescence. B, Flower in front view. C, Longi- 

 tudinal section. 



