SPADICTFLOR.E. 307 



Africa), generally known as " Calla," and Momtera deliciosa many other 

 species are grown in greenhouses. 



Order 6. Lemnaceae (Duck-weeds). These are tlie most 

 reduced form of the Spadiciflorte. They are very small, free- 

 swimming water-plants. The vegetative system resembles a small, 

 leaf-like body (Fig. 303/-/), from which roots hang downwards; 

 this branches by producing a new, similar leaf-like body, which 

 springs from a pocket-like hollow (indicated by a dotted line in 

 the figure) on each side of the older one, at its base (or only on 

 one side). The branching is thus dichasial or helicoid (Fig. 303 A, where 

 /i /')/">/"' indicate shoots of 1st, 2nd, 3rd, 4th generations respectively). The 

 leaf-like bodies are, according to Hegehuaier, leaf-like stems, and thus Lemna 



FIG. 303. Lemna: A vegetative system ; ~B portion of a plant with flowers ; one stamen 

 find tip of the carpel project ; the remaining portions being indicated by the dotted line. 



has no other leaves than the spathe and the sporophylls ; according to the in- 

 vestigations of Engler they are sterns whose upper portion (above the " pocket ") 

 is a leaf, which is not sharply separated from the underlying stem-portion. 

 The inflorescence is a very much reduced Araceous-spadix, consisting in Lemna 

 of 1 or 2 stamens of unequal length (1-stamened <J-tiowers), 1 unilocular 

 carpel ( 9 -flower), and 1 thin spathe (B). [The same is found in Spirodela 

 polyrrhiza, etc. , whose daughter-shoots begin in addition with 1 basal-leaf. 

 Wolffia arrhiza, etc., have no roots, no spathe, and only I <$ -flower in the 

 inflorescence (Engler).] On the germination of the seed a portion of the testa 

 is thrown off as a lid, so that an exit is opened for the radicle. 19 species. In 

 stagnant fresh water, both Temp, and Tropical. In Europe the species are 

 Lemna minor, trisulca, gibba ; Spirodela polijrrlnza, and Wolffia arrhi~a, the 

 smallest Flowering-plant. 



