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A TEXTBOOK OF THEORETICAL BOTANY 



process. Here there are a number of separate flowers closely grouped to- 

 gether, which discharge their pollen in such a position that it could readily 



be transferred from one flower 

 to another by a mollusc crawling 

 across the inflorescence. Indeed 

 it is among the Compositae that 

 most of the recorded cases occur. 

 For example Ludwig has 

 observed small slugs pollinating 

 the capitula of Chrysanthemum 

 leiicanthemum (Oxeye Daisy) 

 (Fig. 1230). It should be pointed 

 out, however, that these obser- 

 vations were made in damp 

 weather when insect visitors 

 were absent and it should not be 

 regarded as the normal method 

 whereby this plant is pollinated. 

 Several instances have been 

 cited of slugs and small snails 

 seeking refuge from inclement 

 weather by crawling into the 

 spathes of certain Aroids. In 

 the course of their wanderings 

 they can effect pollination in 

 much the same way as do small 

 flies (see p. 2017). There is, 

 however, no evidence that the 

 structures clearly suitable for 

 trapping flies are in any way 

 connected with visits by slugs. 



Fig. 1230. — Chrysanthemum leiicanthemum. 

 cophily. Capitulum visited by a slug. 



Mala- 



2. Water Plants 



The part played by water snails is rather different, for here there is some 

 evidence that their activity does normally promote pollination. It has been 

 repeatedly claimed that water snails are responsible for the pollination of 

 species of Lemna. Observations on the pollination of the Duck Weeds is 

 rendered particularly difficult because of the infrequency of flowering. The 

 inflorescence is monoecious. The male flower consists of a single stamen, 

 while the female flower is represented by a gynoecium consisting of a single 

 carpel with 1-6 ovules. Each inflorescence is composed of one female 

 flower and two males, the male flowers sometimes maturing before the 

 stigma is ripe. Observations on this point are, however, contradictory, and 

 it appears to differ in plants growing in different localities. Some observers 

 find that one of the male flowers matures before the female, while the second 

 anther discharges pollen only after the style has died. The pollen grains 



