SNAIL- AND SLUG-POLLINATED PLANTS 79 



tion is out of the question, and that pollen can only be transferred by 

 snails. 



Warming (Jahrb. Bot., Leipzig, iv, 1883, pp. 328-40), who made his obser- 

 vations at Lagoa Santa, traverses this view and argues that snail-pollination is 

 impossible owing to 



1. The rarity of snails in the locality mentioned (Lagoa Santa). 



2. The isolated occurrence of the plant there. 



3. The short flowering period, and the extremely rare occurrence of several 

 spadices blooming on the same plant. 



4. The discharge of carbonic acid gas observed by Ludwig within the spathe. 



Warming establishes the fact that at the time of pollination a sticky juice is 

 secreted, so that even dry-bodied animals can effect polHnation. He is of opinion 

 that fertilization is effected by pollen of the same spadix. 



In opposition to this view of Warming, Ludwig holds (Kosmos, i, 1884) that 

 the observations of the former were carried out in a place where the plant occurs 

 very sporadically in the tops of tall forest trees, and therefore not in sufficient abun- 

 dance to attract the characteristic agents of pollination. 



Ludwig accepts the supposed occasional malacophily of our native Lemnaceae : 

 snails (and insects) wandering about on the patches of duckweed break off pollen- 

 grains and bring them to the concave stigmatic surface. This plant does not need 

 to employ any special allurement ; without any display, and without any other 

 inducement than a firm substratum, it achieves what ' flowers ' achieve by beauty, 

 honey, pleasant odour, &c., which at times serve to attract unbidden guests. Duck- 

 weeds like Aroids (according to Stahl, 'Pflanzen und Schnecken,' Jena, 1888) are 

 protected by raphides against the attacks of snails (cf. Ludwig, 'Lehrbuch der 

 Biologic der Pflanzen,' p. 544). 



In a few European species pollination by snails actually occurs as well as 

 pollination by insects. E. Warming (Bot. Tids., Kjobenhavn, ii, 1877) observed, for 

 instance, that the inflorescences of Calla palustris', which are chiefly visited by 

 small flies, are also frequented by snails which, crawling up on several inflorescences 

 placed one behind the other, transfer pollen-grains that have stuck to the slimy 

 surface of their foot to the stigmas of other plants. Hermann Miiller observed 

 ('Fertilisation,' p. 246) something similar in the case of Chrysosplenium alternifolium. 

 Besides flies, beetles, and ants, he found on numerous flowers small snails (Succinea), 

 some creeping about, others devouring styles or stamens. Pollen-grains were usually 

 to be found in the slimy tracks that occurred on the flowers, and in several cases 

 it was obvious that pollen had been transferred to the stigma by snails. Ludwig 

 (SitzBer. Ges. natf. Freunde, Berlin, 1889, pp. 16-18) observed that Chrysan- 



1 In the garden of the Ober-Realschule at Kiel, I observed (on August 4, 1897) a young 

 specimen of Helix hortensis on the flowers of the species described as Calla maculata. The snail 

 crawled about on the inflorescence, and examination of its foot showed the presence of pollen-grains, 

 so that the possibility of the transference of pollen by snails is proved for this Aroid too. I observed 

 at the same place (on September 23, 1897) the small slug Limax cinereus(?) among the flowers of 

 Colchicum autumnale. It devoured the perianth leaves, and in doing so occasionally disturbed 

 anthers and stigma, so that self- or cross-pollination might result. Numerous flowers were almost 

 completely deprived of their perianth by slugs, so that frequent visits may be inferred. 



