THE MONOCOTYLEDONES 1977 



Pollination mechanisms have only been studied critically in a few- 

 instances. 



In Alisma plantago (Fig. 1908) the flowers are arranged in pyramidal 

 panicles and possess yellow nectar guides at the base of each of the three 

 petals. Nectar is secreted as a series of small drops from a fleshy ring 

 formed bv the union of the broadened bases of the six stamen filaments. 



Fig. 1908. — Alisma. Flower to illustrate pollination. 

 See in text. 



These filaments are directed obliquely outwards and the anthers dehisce 

 extrorsely. The styles stand erect in the centre of the flowers. 



The most frequent visitors are hover flies. These, if they alight on the 

 centre of the flower, are most likely to effect cross-pollination. On the 

 other hand, if thev alight on the petal they are more likely to transfer pollen 

 from the anther to the stigma of the same flower. Small bees have also 

 been observed to visit the flowers. 



In the other genera the mode of pollination is less certain. Anemo- 

 philous pollination may occur in Sagittaria, though self-pollination is to a 

 large extent precluded, according to Warnstorf, on account of the monoecious 

 nature of the flowers. In time of floods the flowers of Elisma natans remain 

 closed below the w^ater and are pollinated pseudo-cleistogamically. 



As has been already pointed out, one of the chief interests in the family 

 is the similarity which it shows to the Ranunculaceae. Hutchinson 

 points out that although the absence of endosperm and the peculiar 

 character of the embryo differentiate them from the Ranunculaceae, there 

 are other features which suggest an aflinity between them. He points out 

 that Ranalisma, which was discovered by Ridley in a patch of mud between 

 limestone cliffs in Malaya, differs from Ranunculus only in the solitary 



