50 NATURE STUDY AND AGRICULTURE 



and by experiments. Germination studies should always 

 make clear by experiment the conditions essential to this 

 process, and the varying habits of different seeds. Simple 

 experiments demonstrating the ascent of sap, the evapora- 

 tion of water from the leaves, the rate of growth, and the 

 turning of roots toward water can be arranged with home- 

 made apparatus. One cannot see the sap ascending in a 

 tree, but after experimenting with the movement of water 

 in a stem he can appreciate what is going on in countless 

 tree trunks. One cannot see water vapor arising from 

 leaves, but after measuring transpiration he can appreciate 

 the great volume of water given out by forests, and their 

 value as water reservoirs. 



Definiteness. To work effectively, the teacher must 

 work to some definite purpose. To place material before 

 children, or to send them out to observe anything, without 

 definite knowledge on the part of the teacher as to the things 

 to be done and some plan of action suggested to the children 

 is never effective. Children have been set to observe 

 a tree, with no suggestion whatsoever, and without the 

 faintest idea as to the important points. As an experi- 

 ment to discover what facts about a tree impress children 

 the most, this is sometimes worth while, but as an ordinary 

 method it results in confusion. No material should be 

 assigned that has not been traversed previously by the 

 teacher, so that she knows that there are some very definite 

 facts in plain sight. Even in the university the laboratory 

 instructor must work over his material and his experiments 

 before each exercise, so as to be sure that what he wants is 

 there in good condition or that his experiment will work. 

 Quite as much is this needed^ in nature study, for young 



