22O Minnesota Plant Life. 



or iris and quite different from the great oval leaves of the 

 skunk-cabbage, the small heart-shaped leaves of the calla, or 

 the three-parted leaves of the jack-in-the-pulpit. 



Duckweeds. The duckweeds are small natant or submerged 

 plants which form green scums on pools and puddles. They 

 have no foliage-leaves but develop little flat, oval or triangu- 

 lar stems which float upon the surface of the water. Some 

 of them have roots which hang down as counterpoises, but 

 others are without roots and appear suspended in the water as 

 tiny green ovoid balls not as large as a pin-head. The latter 

 are the smallest of all flowering plants and are marvels of reduc- 

 tion. When the duckweeds flower, which they very seldom 

 do, the stamen and pistil stand together in a little depression 

 on the surface. For the most part these plants depend upon 

 propagation for their persistence and do not reproduce by seeds. 

 In Minnesota there are five or six species. The two kinds of 

 duckweed which are most abundant are the ivy-leaved or three- 

 cornered duckweed and the smaller duckweed. In the latter 

 the floating discs are about an eighth of an inch in diameter 

 and of nearly circular shape. In the former the plant-body is 

 branched more abundantly and builds up a group of three-cor- 

 nered or arrowhead-shaped branches. In each of these plants 

 a single root hangs down from the middle of the plant-body. 



Another somewhat larger duckweed, with discs a quarter of 

 an inch or so in diameter is easily distinguished by the forma- 

 tion of tufts of roots on the under side. In these plants there 

 are traces of an original terrestrial existence, although they 

 have become so much modified by their aquatic life that they 

 now resemble some forms of algae. Nevertheless the roots in 

 all the species which produce these organs are supplied with 

 root-caps, structures of value to all terrestrial plants, because 

 they protect the young roots as they penetrate the soil. They 

 are, however, of no value to aquatic plants and some aquatic 

 plants shed their root-caps. The little floating fern of Minne- 

 sota is interesting from its general habit of dispensing with the 

 root-caps shortly after the roots have begun to extend into the 

 water. But when plants like the floating fern or the duck- 

 weed develop roots with caps and afterwards drop these caps, 

 now become useless, into the water, it may be assumed that they 



