Fig. 288: Spirodela polyrhiza: a, habit, showing group of fronds, each with nu- 

 merous roots, X 2; b, fronds producing buds, top view, showing the conspicuous 

 nerves radiating from the reproductive pouches, X 4; c and d, fronds (longitudinal 

 section), showing air chambers, X 4; e, winter bud, X 12; f, fronds, lower surface, 

 showing the slender stipes by which they are attached to one another and the clustered 

 roots, X 3; g and h, root tips, with and without rootcaps, the rootcap 0.9-1.5 mm. 

 long, X 20. (From Mason, Fig. 164). 



closely resembling in size and shape some species of Lemna; dorsal surface yellow- 

 green, flat to convex; ventral surface convex, frequently somewhat inflated, com- 

 monly red-purple-pigmented. 



On lakes and ponds, rare in e. Tex. (Shelby Co.); in the Far East, S. Pac. 

 and U. S. 



2. Lemna L. 



Duckweed. Duck-meat 



Diminutive free-floating aquatics or growing on wet surfaces; thallus solitary 

 or in groups of 2 or more, with 1 to 3 nerves and a single root without vascular 

 tissue, bearing on either side a meristematic pouch in which are vegetative and 

 flower buds; vegetative buds usually disarticulate to form independent plants (in 

 L. trisulca often remaining attached); flowers unisexual, produced in a mem- 

 branous spathe; staminate flowers usually 2 to a spathe, each flower consisting 



565 



