MARE'S-TAIL-TRIBE. , 217 



water ; frequent. An aquatic plant, forming a tangled 

 mass of slender, much, branched stems ; leaves 4 in a 

 whorl, finely divided into numerous hair-like segments, 

 the whole plant being submerged, except the spikes of 

 inconspicuous greenish flowers, which rise a- few inches 

 above the surface. FL July, August. Perennial. 



MYRIOPHYLLUM spiCATUM (Spiked Water Milfoil). 



* M. vertidllatum (Whorled Water Milfoil) differs 

 from the preceding in having the flowers in whorls at 

 the base of the leaves ; M. alterniflorum (Alternate- 

 flowered Water Milfoil) has the barren flowers alternately 

 arranged in a short leafless spike, with i\iz fertile flowers 

 about 3 together, in the axils of the leaves, at its base. 

 The last two are rare. 



