PLANTS FOE. 29 



give out the pure vivifying oxygen. Although 

 so commonly cultivated in this country, it is a 

 native of the south of Europe, where it flourishes 

 in quick-running streams. It is what botanists 

 call a dioecious plant, that is, its stamens 

 grow on flowers on one plant, whilst its pistils 

 grow on flowers on another plant. Pistil- 

 liferous plants are mostly seen in this country. 

 The flowers grow on the summit of a long spiral 

 * flower-stalk, which is sometimes several feet in 

 length. The object of this long flower-stalk is 

 very curious : the stamen-bearing flowers, when 

 ripe, break off, and float to the top of the water, 

 and if the pistils had not very long stalks in the 

 deep rivers in which they grow, the fructifying 

 pollen of the stamen would never come in con- 

 tact with them. No sooner has this process 

 taken place on the surface of the water, than 

 the long spiral stalk contracts, and the newly- 

 formed seeds in the pistil are drawn down into 

 the soil, where they may germinate and produce 

 new plants. The Valisneria was first cultivated 

 generally in a domestic manner, in this country, 

 on account of the cellular tissue of which its 

 leaves are composed, exhibiting under the 

 microscope a circulation of their contents. This 

 movement can only be seen by cutting away 

 from the surface of the leaf a portion of the 

 cellular tissue, so as to render the rest more 

 transparent. The same kind of circulation may 

 now be seen in a great number of plants. 

 Valisneria belongs to an order of plants called by 

 Lindley Hydrocharads (Hydroclttiridacece), and 

 to this family some other plants belong, which 

 will be found useful in the Aquavivarium. 

 ANACHARIS ALSINASTRUM, the New Water Weed or 

 Water Thyme, is one of these (Fig. 7). This plant 



