DUCKWEED 



193 



opposite end pointed. The two- sides are seldom 

 quite symmetrical. A ridge extends along the upper 

 surface from the round to the pointed end, some- 

 thing like the ridge on a house-roof, but not 

 nearly so sharp. From each frond a thread-like root 

 hangs down into the water. The root ends in a 



FIG. 55. Duckweed (Leinna tninor), magnified. A, single frond ; a, scar of 

 attachment to parent. A ridge extends from a to b across the upper surface of 



out two new 



the frond, gently subsiding towards b ', B, frond, budding 



fronds. C, longitudinal section. D, transverse section. All the figures are 



diagrammatic. 



root-cap, which has long been a very familiar object 

 of study in every botanical laboratory. 



We call the green discs of Duckweed fronds and 

 not leaves, because they bear roots and flowers. 

 Functionally they are at once leaves and stems. 

 During the summer they bud continually. A pair of 

 minute rudiments appears on the upper surface of a 



O 



