AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 



5S 



Fig. 12. — Lemna 

 polyrrhlza. 



Each consists of a small green, more or less oval 

 leaf or frond floating on the water, with one or more 

 rootlets hanging from beneath, but never taking root 

 in the mud. Usually two, three or four 

 fronds are attached together, so as to 

 form an irregular star. . Lemna polyrrhiza, 

 the "many-footed Lemna" (Fig. 12), has 

 the largest fronds, is a deeper green, and, 

 as its specific name signifies, has many 

 rootlets, often a dozen, hanging in a clus- 

 ter from each. It can always be recog- 

 nized by this root-cluster and by the dull 

 purple color of the lower surface. It seems to like 

 the sun better than Lemfia minor, and is oftener found 

 abundantly on open ponds, while the latter appears to 

 prefer ditches with high banks and shade. 



Lemna minor (Fig. 13) has smaller, more oval and 

 thinner fronds. It is lighter green in color, the lower 

 surface is never purplish, and it has but one 

 rootlet to each frond. Both species have a 

 peculiar little cap on the free end of, each 

 rootlet, where it is more easily seen with 

 the naked eye on Lemna polyrrhiza, as it is 

 there usually darker than the rest of the 

 rootlet. 



There are several other species, but 

 they, are- so seldom found that they need 

 not be included in this list. They all 

 multiply by the growth of young fronds 

 from the edges of the old and mature, this accounting 

 for the clusters so commonly seen. They also bloom, 

 but the flowers are extremely small and are rarely ob- 

 served. The student will be fortunate to find speci- 



