18 THE AQUAVIVARIUM. 



the Grass-wrack (Zoster a marina) will not grow 

 unless there is mud at the bottom of the vessel. 

 The beautiful Aponogeton, from the Cape, will not 

 grow in a shallow soil. Many of our common ditch 

 plants, whose leaves and flowers float upon or grow 

 above the water, as the Water Plantain (Alisma 

 Plantago), the Water Violet (Hottonia palustris), 

 the white and yellow Water Lilies (Nymphcea alba 

 and Nuphar luteum), with many others, require a 

 considerable depth of soil in order to retain them 

 in their positions ; in fact, when plants have a large 

 surface of leaves and flowers, and live in running 

 streams, it is necessary that they should have rope- 

 like roots and deep mooring-grounds. It is yet a 

 question, whether such plants take up much nou- 

 rishment by their roots, anc^ what it is ; at any 

 rate it is a well-known fact, that many water- 

 plants will continue to grow and increase without 

 their roots being immersed in the soil at all : such 

 plants are the New Water-weed (Anacharis Alsi- 

 nastrum)j the Yalisneria (Valisneria spiralis), the 

 Water Crowfoot (Ranunculus aquatilis), the Star- 

 worts (Callitriche), the species of Chara, and many 

 others. Many of the Confervse, the species of Duck- 

 weed (Lemna), the Water Chestnut (Trapa natans), 

 Pontederia crassipes, and others, although they 

 have roots, are seldom or never found with them in 

 the soil. 



Under these circumstances, it will be found that 

 the nature of the soil is not a matter of much 

 importance to the plant, and therefore the conve- 

 nience and beauty of the Aquavivarium may be 

 consulted. For cleanliness, and all the purposes of 

 the plants mostly cultivated, a soil composed of 

 well-washed river sand will be found to answer 

 best : this may be put at the bottom of the jar, 

 mixed with a few small pebbles, to the depth of 



