80 LEMNACEAE [CH. 



Wolffia, the third and last genus of the Lemnaceae, enjoys 

 the distinction of including the most minute of all flowering 

 plants. The tiny, simple fronds are devoid of roots. The species 

 which occurs in England, Wolffia Michelii, Schleid., has fronds 

 which in no dimension exceed I -5 mm., while W. brasiliensis, 

 Wedd., is described as being only one-half to two-thirds of this 

 size. Its discoverer, Weddell 1 , records that about twelve flower- 

 ing individuals of this tiny species could be accommodated upon 

 a single frond of Lemna minor. He noticed this little Wolffia 

 growing in the neighbourhood of that most gigantic of aquatics, 

 Victoria regia, the Waterlily of the Amazons, and their propin- 

 quity drew from him the exclamation, "Singuliere bizarrerie 

 de la nature d'avoir seme ensemble ces deux vegetaux! " Our 

 native species winters at the bottom of the water, its minute 

 fronds being just sufficiently weighted with starch grains to 

 induce sinking. 



The flowers of the Lemnaceae are reduced to the simplest 

 possible terms. Spirodela polyrrhiza^ (Fig. 47, p. 74), for 

 instance, has an inflorescence consisting merely of a spathe 

 (j/>.) enclosing two male flowers each represented by a stamen 

 only (st-i and J/ 2 ) and a female flower simply formed of a gynae- 

 ceum (c.) with one or two ovules. Lemna minor 3 , and probably 

 other members of the family, appear to be pollinated by insects. 

 The essential organs are raised above the water level, but they 

 are short and stiff, while the pollen is scanty, so anemophily 

 seems improbable. Small beetles and aquatic insects have been 

 observed crawling about among the flowering fronds, which are 

 markedly protandrous. 



The seeds of the Lemnaceae, in the relatively rare cases in 

 which they are produced, may germinate as soon as they 

 are ripe in the summer sometimes even while attached to the 

 parent plant but in other cases they may rest through the 

 winter and defer germination until the spring 4 . Fig. 52 

 illustrates the seedling stage of Lemna trisulca. 



1 Weddell, H. A. (1849). 2 Hegelmaier, F. (1871). 



3 Ludwig, F. (1881). 4 Hegelmaier, F. (1868). 



