12 WHY AND HOW WE STUDY BIOLOGY 



becomes too rapid. Add more snails if the sides of the aquarium 

 become covered with a green growth. In this way, your aquarium 

 will be kept in balance, which means that the plant life supplies the 

 animals with food in sufficient quantity while the animals give the 

 plants enough wastes to allow them to make food in the sun- 

 light. The interesting story of how plants do this will be told 

 later. 



Other interesting problems. Out of the field trips and the 

 collecting of insects and other animals will come many other 

 instructive problems. Some pupils may become interested in the 

 classification of animals, others in making a survey of the locality 

 to see where different animals are most plentiful, and others in the 

 various ways in which animals protect themselves or are protected 

 by their surroundings. In fact, there are so many problems that 

 it will be almost impossible for us to note them all here. Let us 

 now turn to some plant problems or projects that will come out of 

 a fall field trip. 



Plant studies in the field. The fall of the year usually finds a 

 good many plants in blossom, although most of these have com- 

 posite blossoms. But flowers are not the only things to collect. 

 A leaf collection can easily be made in the fall and mounted in the 

 way suggested for insects, except that no wood need be used be- 

 tween the plates of glass. Interesting mounts of skeleton leaves 

 may be prepared by placing collected leaves in trays of water until 

 the leaf tissue has rotted away, leaving the skeleton of veins and 

 ribs as a delicate tracing. These make valuable aids in the 

 laboratory study of leaves. Another interesting and easy method 

 of obtaining good leaf illustrations for your notebook is to make 

 blue prints of them. Weed and flower collections may be mounted 

 in a similar manner. 



Some members of the class may become interested in making 

 a collection of weeds, and some may wish to make a survey of 

 weeds found in their locality. Weed eradication may be studied 

 as well, thanks to the various government pamphlets which are 

 easily obtainable. Many of us do not even know the trees com- 

 mon to our neighborhood. A survey of trees might be conducted 

 to determine where different types may be found and then sug- 



