INTRODUCTION IX 



It is advisable to use a separate loose sheet for each 

 question or experiment. The drawings should be inked 

 with India ink; this can be done outside the class 

 room: a drawing ^^w is not necessary — any good fino 

 pen will do. A single bottle of India ink will supply 

 a class, as very little is used. 



Where each experiment is to be done by each indi- 

 vidual, a laboratory is necessary: where each is to be 

 done by a group or section of the class, only a limited 

 space is needed : where each is done by the class as a 

 whole, a single shelf in front of a window and a 

 drawer beneath to hold the utensils will suffice. For 

 most of the experiments such plants have been sug- 

 gested as will grow even with poor light and under 

 discouraging conditions. This is an especially impor- 

 tant consideration, in view of the fact that the average 

 schoolroom is a very poor place to grow plants. 



While the microscopic work suggested is of the 

 simplest kind, it may often be necessary to restrict it 

 to demonstrations only or to omit it altogether. 



The principle involved is the thing of prime impor- 

 tance in all the experiments. Exact quantitative 

 results are not necessary, nor is it desirable at this 

 stage to spend much time or effort in trying to obtain 

 them. 



It may be added that practically all the experiments 

 have been successfully tried in the schools, many of 

 them in the lower grades. 



