AMPHIBIOUS KNOTGRASS 



129 



are short, and ripen before the stigma, the former being proterandrous. 

 When growing in water it is protected from ants or flying insects, so 

 that the stem is smooth. When growing on land it is densely hairy 

 with sticky glands, so that small insects cannot crawl up the stems, an 

 adaptation for the promotion of cross-pollination. 



There are two forms of flowers; in the one case the pistil is long 



AMPHIBIOUS KNOTGRASS (Polygonum amphibium, L.) 



and the stamens are short, and there are other flowers with a short 

 pistil and long stamens. Pistillate flowers also occur. 



The fruit is partly enclosed in a perianth, and may be blown to 

 a distance to fall in the water and be thus dispersed by it. If aquatic 

 it needs no special soil, if on land it is usually a clay-loving plant 

 addicted to a clay soil. 



A fungus, Pnccinia polygoni, attacks the leaves, and it is galled 

 by Cccidomyia persicarice, causing the leaves to curl. A beetle, 



VOL. IV. ' 55 



