CELLULAR ANATOMY OF THE STEM 221 



each watering. By placing the plant under different con- 

 ditions of light, heat, etc., the effect of those conditions upon 

 transpiration may be determined. The larger the plant, i.e. 

 the more leaf surface, the better, since the weighings may then 

 be relatively more accurate. Instead of the glass jar the 

 plant may simply be wrapped in rubber, but as this does not 

 permit the earth to be seen, there is danger of giving too much 

 or too little water, to the great detriment of the results of the 

 experiment. There are many other ways described in various 

 books, of measuring the amount of water removed in transpira- 

 tion, but none are so satisfactory as weighing. 



Transpiration is of great importance, both physiologically 

 and ecologically, and should be discussed fully by the teacher. 

 As in other experiments, as much of the work as possible 

 should be done by the students. The fact that it, like 

 photosynthesis, has no equivalent in the animal economy, 

 should be emphasized. Probably its chief use to the plant 

 is to enable it to lift mineral matters from the soil into the 

 leaves where they are needed. 



XII. The Cellular Anatomy of the Shoot - the 



Stem in Particular 



43. What is the cellular structure, and what tissue 

 systems are represented in typical stems of 

 the higher plants ? Since stems fall, as to their 

 structure, into two distinct types, it is neces- 

 sary to select representatives of each. 



What is the cellular anatomy of the Corn stem ? 



What is the distribution of its tissue systems ? 



