ANIMALS OF POND AND STREAM 37 



in hand and squeeze it to get in more of the dry cement. Keep the hands 

 powdered with the latter. Work it to the consistency of putty. 



With the putty-knife lay a rim of this cement around the edge of the 

 8 by 10 glass. Press this, cement rim down, into the frame for the bottom 

 of the aquarium. Trim off the excess of cement. Similarly set the 6 by 10 

 pieces for the sides and then the 6 by 8 pieces for the ends. Roll out ropes 

 of the cement and press these into all the angles where glasses meet. Let 

 stand for twenty-four hours; it may then be used, even though the cement 

 is not hard. 



The balanced aquarium. The aquarium is to be stocked with plenty 

 of water plants and a few animals. A couple of minnows, two or three 

 dragon-fly nymphs, and a couple of snails are enough animal life for one 

 aquarium. Keep the top covered with a piece of glass to prevent evapora- 

 tion. The water does not need to be changed except as it becomes very 

 dirty. When plenty of plants are present they will give off an abundance 

 of what the animals need. What is this ? The animals will supply what 

 the plants need. What ? Under such conditions the aquarium is balanced. 

 The following are some of the best of the plants to use in the aquarium. 

 Make a sketch of enough of each so you can recognize it and remember it. 

 Cabomba, water milfoil (Myriophyllum), hornwort (Ceratophyllum), 

 bladderwort (Utricularia) , water buttercup (Ranunculus aquatilis), ditch 

 moss (Elodea), eelgrass (Vallisneria), pondweed (Potamogetori). These 

 water weeds, all flowering plants, are themselves very interesting. Note 

 that the leaves are long, slender, and thin or else very much cut up so their 

 parts are threadlike. Can you tell why? The water buttercup often 

 grows partly in the water and partly out, when the leaves are of two sorts. 

 What are they and what is the significance of their varied form ? 



