102 THE PLANT WORLD 



Our Teachers' Department. 



Edited by Professor Francis E. Lloyd, 



Teachers College, Columbia University, j\ew York City. 



THE STUDY OF LEAVES. 



Teachers of nature study will read with interest the article which we 

 print in this issue, by Miss Jean Broadhurst, of the New Jersey Normal and 

 Model Schools. In it is described a successful attempt to get a class of boys 

 to study the leaves of trees in an independent, virile manner, and to learn, 

 not merely to use an analytical key, but to make one. Miss Broadhurst 

 is to be commended for giving an inductive account of what was actually 

 done in her class-room, and she shows that it is possible to make the 

 subject which was taken up a real problem rather than a memory 

 exercise. 



We should be glad to publish the results of similar attempts by other 

 teachers. 



IMPROVEMENT OF OXYGEN DETERMINATION METHOD. 



In our last issue we described a method of oxygen-determination as 

 used by Professor H, M. Richards. In the last sentence we stated that 

 "the greater W'Cight of the mercur>^ column introduces a slight error, 

 which however may be disregarded." This however is true only when 

 the mercury column is short (two to three inches) and will rapidly become 

 greater as the column lengthens. Recently, however. Professor Richards 

 has perfected the manipulation so as to eliminate this error. 



When the gas has been collected in a closed tube over mercury, close 

 the open end tightly with the thumb, and, holding the whole under water 

 in an oblique position with the closed end the lower, allow so much 

 water as will enter the tube. One must be a little careful in order not 

 to lose the gas, and this is done by removing the thumb only just enough 

 to allow the water to enter. The negative pressure is thus released. 

 Keeping the tube tightly closed with the wet thumb, mark the amount 

 of the gas sample by sticking a label on the outside of the tube. Proceed 

 to apply the pyrogallol test and note the diminution of the volume of gas. 



ANOTHER METHOD OF OXYGEN DETERMINATION. 



For the purpose of demonstrating the liberation of oxygen by plants 

 I always use the freshest-looking leaves which can be found in the woods 

 at the time of year when they are needed. Ash leaves work well, and 

 the best results have been obtained with some butternut leaves that came 

 up late from the stump of a recently-felled tree. The leaves were packed 



