THE AQUARIUM. 97 



possible, this should consist of a pound or two of mud or clay 

 from the bottom of a pond. This will probably contain many ova 

 or larv?e, which will develop in due course into interesting objects. 

 If this be not procurable, a good layer of silver sand will suffice. 

 This should be covered to the extent of about an inch with red 

 gravel, which in its turn should bear a stratum of about half-an- 

 inch of larger stones and a few empty clean shells. A little tap- 

 water should then be syphoned on, and the aquarium is ready for 

 its plants. 



Of all plants, none, in our experience, excels the common 

 American pond-weed, Elodea canadensis (formerly called Anacha- 

 ris). This plant will grow anywhere with the greatest profusion ; 

 it need not be rooted ; a few sprigs thrown into the water will 

 speedily send down roots of their own accord. So luxuriantly does 

 it flourish, that it will generally require a little judicious pruning to 

 keep it within bounds. Another excellent plant is Ceratophyllum 

 submersum, the hornwort. This should he taken with the roots 

 and planted ; it will then live for years. It frequently has adher- 

 ing to the leaves the interesting rotifer, Melicerta ringens, and also 

 sometimes the lovely Stephanoceros eichornii, which, to the owner 

 of a microscope, will be an unfailing source of pleasure. The 

 common pond-weed, Potoniageton heterophyllus, the perfoliate pond- 

 weed, P. pe7'foHatiis^ also P. pectinafus, are useful and attractive 

 plants. All may be found in the canals round London or in the 

 country. A root or two of the water crawfoot, R. aquatilis^ will 

 also grow well, and give a beautiful effect with its finely divided, 

 fennel-like, submersed leaves. If taken when in flower in the 

 early . summer, it will continue to bloom for weeks, the elegant 

 white flowers being as attractive in appearance as those of a rare 

 exotic. A few plants of one of the duckweeds may be usefully 

 included ; but too many should not be introduced, as when their 

 location suits them they increase by budding very fast. The great 

 duckweed, Lenma polyrhiza, and the ivy-leaved duckweed, Lemna 

 trisidca^ are preferable to the other species, being neater and not 

 so prone to decay and leave unsightly withered fronds. 



Having introduced the plants, rooting such as have roots, and 

 placing a few small stones over the soil to prevent them from 

 dragging their anchors, the aquarium should be placed where it is 



International Journal of Microscopy and Natural Science. 



Third Series. Vol. V. h 



