io6 
THE ESSEX NATURALIST. 
Another member of the family Alismacece bearing leaves 
of different shapes, is the Arrowhead, Sagittaria sagittifolia , 
a plant common in canals, and slow streams, and abundant 
in the Roding. The floating leaves are oval, and the aerial leaves 
arrow-shaped. The submerged leaves are ribbonlike and trans¬ 
lucent with blunt rounded ends, and may grow to be a yard long. 
Where the current is too swift for the arrow-shaped leaves to 
grow, these submerged ribbons often form great beds swaying 
in the stream, and may be puzzling to identify unless an arrow 
leaf is near by to give a clue. With a lens they may be 
distinguished from other ribbon-leaves by the venation. The 
midrib is slightly emphasized and usually there are two parallel 
lateral veins, from which oblique branches are given off, espec¬ 
ially near the tip. One side of the leaf has a tendency to grow 
more vigorously than the other, the result being that the leaves 
often have a slight spiral twist. The whorls of large flowers 
with white, purple-based petals, purple anthers and golden 
pollen are probably familiar to all of us ; the stamens and pistils 
usually grow on different flowers ; the spiky balls of ripe fruit 
roughly resemble those of Bur-reed. In autumn reserves of 
food are stored in the corm at the base of the stem and also 
in tubers borne on long underground runners. These tubers 
are striking-looking objects ; they are round, peacock-blue 
