THE ANGIOSPERMAE 1303 



Pollination by larger birds, including some of the smaller Woodpeckers 

 and Starlings, has been recorded in several instances, for it is known that 

 these birds are attracted by sweet juices and it is not improbable that they 

 would be attracted by nectar as well. 



Quite apart from such examples, a considerable number of insect- 

 catching birds may perform pollination in cases like that cited above where 

 insects are attracted to the nectar, but owing to the shape of the flower, 

 would not themselves perform pollination. The modifications of structure 

 in a flower or an inflorescence which produce such a complicated indirect 

 pollination mechanism are difficult to interpret and it will require a far more 

 critical and extended study of the subject in the tropics before the full storv 

 can be given. When it is unfolded it is probable that, not only will the 

 number of examples be greatly increased, but the variety of mechanisms will 

 require a more elaborate grouping than is possible at present. 



C. Slug and Snail Pollination (Malacophily) 



To what extent slugs and snails actually perform pollination is a matter 

 of some doubt. It is true that their slime trails on examination have been 

 found to contain pollen grains. It is therefore reasonable to assume that, 

 if the animal crawls from the anther to the stigma of a flower, it may trans- 

 fer the pollen to the stigma. Such a pollination is, however, fortuitous and 

 there is no evidence that flowers are in any way specially modified to assist 

 the animal to perform pollination. Indeed the activity of slugs and snails 

 being what it is, it seems likely that in general the harm they do to plants 

 exceeds any beneficial pollination which they may occasionally efl^ect. 



It is difficult therefore to consider slug or snail pollination from the same 

 standpoint as other types of animal pollination. There are few, if any, 

 structural adaptions on the part of the plant which can be considered to 

 promote this method of pollination. Many flowers for one reason or another 

 cannot be pollinated by these animals because the shape of the flower is 

 unsuitable. A possible exception is the well-known Aspidistra liirida, an 

 East Asiatic plant whose flowers are produced from below the ground and 

 open level with the surface of the soil. The stigma forms a large flat plate 

 almost filling the opening of the perianth and seems well suited to molluscan 

 pollination, but it cannot be said with certainty if this is the normal process. 

 There is no evidence that Molluscs are attracted by sugary secretions, nor 

 that any tissues are developed which specially attract them. On the other 

 hand very damp, rainy weather, when slugs and snails abound in vegetation, 

 is just the weather most unsuitable for insect visits. Plants, therefore, which 

 are in flower at such times, might fail to receive insect visits but might, if the 

 shape of the flower were suitable, benefit from the visit of a slug or a snail. 



I . Land Plants 



The most suitable type of flower for these animals is one which is as flat 

 as possible and in which the anthers project but little above the rest of the 

 organs. The capitulum is obviously a very suitable arrangement for this 



I 



