78 INTRODUCTION 



(f) Plants with Snail-pollinated or Slug-pollinated Flowers, 

 Malacophilae (M). 



The possibility of snails or slugs efTecting pollination arises when small flowers 

 are crowded together at the same level, and in the case of flat flowers with stigmas 

 and anthers which project but little. It is then possible for such creatures when 

 creeping over the flowers or inflorescences, to transfer pollen-grains which remain 

 clinging to the slimy surface of their foot to the stigmas of the same plant, or 

 even to those of others. In most cases, however, snails or slugs are only the 

 occasional and not the exclusive agents of pollination. 



The first contribution to our knowledge of malacophilous plants was made 

 by Delpino (' Ulter. osserv. sulla dicog. nel regno veg.,' Atti Soc. ital. sc. nat., Milano, 

 xi and xii, 1868 and 1869, pp. 238-40) when he described the pollination of Rohdea 

 japonica (? Asparagineae) by Helix aspersa, H. vermiculata, and others. Hermann 

 Miiller (' Fertilisation,' p. 551) summarizes the passage as follows : — ' This plant 

 seems to be transitional to the Aroideae, for it possesses a kind of spadix with crowded, 

 flattened flowers arranged in an unbroken spiral. The flattening of the margin of 

 the perianth to exactly the same level as the tips of the anthers and stigmas led 

 Delpino to suspect pollination by animals creeping over the flowers, and he actually 

 observed snails (Helix aspersa, vermiculata, and others), each of which consumed 

 greedily the yellow perianth, which is fleshy at the time of flowering, of about ten 

 flowers belonging to any particular spadix, and then visited another inflorescence. 

 Only the flowers touched by snails were fertile ; the plants appeared infertile as 

 regards their own pollen. There can be no doubt from these observations that 

 snails are active agents of pollination. 



Delpino (op. cit., pp. 235-8) suspected that Alocasia odora is also pollinated 

 by snails ; the entire length of spadix, according to Hermann Miiller's paraphrase 

 ('Fertilisation,' p. 564), is beset with normal and reduced female and male flowers. 

 Only the female flowers are enclosed in the lower dilated part of the spathe, and they 

 are the first to ripen. There is only a narrow passage by which snails can creep into 

 the space surrounding the stigmas, into which they are tempted by the diffusion of 

 an agreeable odour. Even this entry is closed in the second stage of flowering, at 

 which time the anthers dehisce. Snails which visit flowers that are in this second stage 

 seek admission in vain, covering themselves however with pollen, which they deposit 

 on the stigmas of younger flowers to which the approach still stands open. After the 

 snails have discharged the important work of cross-pollination, Delpino states that 

 they are killed by means of an irritant juice in the space that encloses them, being 

 thus prevented from devouring the flowers. 



Delpino also supposed that there was occasional transfer of pollen by snails in 

 Amorphophallus variabilis, species of Anthurium, Arisaema filiforme, Atherurus 

 tripartitus, and Typhonium cuspidatum. 



Ludwig (Kosmos, vi, 1882, pp. 34 et seq.) observed and investigated at Greiz 

 greenhouse specimens of Philodendron pinnatifidum Schott., and believes that this 

 plant is pollinated by snails. The entire floral arrangement agrees in many points 

 with that of Rohdea japonica and Alocasia odora, which Delpino has described as 

 snail-pollinated. Ludwig points out that in Philodendron pinnatifidum self-pollina- 



