AMPHIBIOUS KNOTGRASS 



129 



are short, and ripen before the sii;4ma, the former beino' protenuuh-ous. 

 When yrowin;;- in water it is protected from ants or Hying insects, so 

 tliat the stem is smooth. When gTowing on land it is densely hairy 

 with sticky glands, so that small insects cannot crawl u[) the stems, an 

 adapteition for the promotion of cross-pollination. 



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



riiuuj i .aU^i:. .S. Garin.-U 



A.MPHIBIOl'S K.SOTGUASS (Po/ygiinuill uillplliliiiail, 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, Pitccinia polygoni, attacks the leaves, and it is galled 

 by Cecidoniyia persicarice, causing the leaves to curl. A loeetle, 



VOL. IV. 



55 



