266 THE STORY OF PLANT LIFE 



like that of Water Milfoil, with which it might be 

 confused, had not the latter, as a rule, a more robust 

 stem, and a different green tinge and pinkish or 

 purple stems and pectinate foliage, with a pink rachis. 

 The leaves are in whorls, forked twice or three times, 

 with distant teeth or spines. The segments are 

 linear to awl-like, spreading, and the leaves are dark 

 green. The segments of the uppermost leaves are 

 broader and flatter, more rigid. 



Apparently the flowers are only formed in shallow 

 water, a fact which has to do probably with the 

 thermal constant and the possibility of effective 

 pollination. The plant is monoecious. The flowers 

 are very small, and have no peduncle, being borne in 

 the axils of the whorled leaves. A whorl of very 

 small involucral bracts encircles each. There is no 

 perianth, unless the bracts be regarded as a sepaloid 

 perianth. There are twelve to twenty oblong anthers 

 in the male flowers on a convex receptacle. They 

 have no stalks. The female flowers, surrounded by 

 nine to ten sepaloid bracts, hypogynous, consist of a 

 small ovoid ovary, with a simple terminal style. 

 The pistil is slender and sticky. There is a single, 

 pendulous, orthotropous ovule. The fruit is an 

 ovoid, flattened achene, which is crowned by the 

 persistent, slender, curved or hooked style. The 

 fruit has no wing, but has a spine on each side near 

 the base; but they may be wanting, and the style 

 may be short, and the surface also may be covered 

 with small points or prickles. 



