MOVEMENTS OP PLANTS. 33 



The proper methods of examining the formation of new cells 

 in a simple case are indicated in the studies upon a stamen-hair 

 of Tradescantia noted on page 380. 



XVIII. MOVEMENTS OF PLANTS. 



The student is advised to select some one plant in a vigorous 

 condition and make a thorough examination of all the phenomena 

 of movement which it presents. The plants named below are 

 among the best for such an examination, and they can be made 

 to grow even under rather unfavorable conditions, like those 

 afforded by schoolrooms. 



Spontaneous movements. Desmodium gyrans, the Morning 

 Glory, or Hop, may be used. The first requires a high tem- 

 perature and a fair amount of moisture in the air in order to 

 exhibit its peculiar movements satisfactorily. 



Movements following shock. The Sensitive plant (Mimosa 

 pudica) should be observed. It can be experimented upon with 

 various kinds of irritants, both mechanical and chemical, at 

 various temperatures, and under the influence of anaesthetics. 

 For the experiments with anaesthetics only very young plants 

 are suitable, and they cannot well be used afterwards for other 

 investigations. 



In the case of all of the above plants note any changes which 

 the leaves undergo during the day and at the approach of 

 night. 



The details given in 1045 suffice to indicate the general method 

 of exaggerating by means of slender glass threads the slow and 

 slight movements of plants, and do not need further treatment 

 here. For observations with such threads, the following plants 

 are very useful : seedlings of the Morning Glory, clover, cress, 

 cabbage, and sunflower. 



XIX. TENSION OF TISSUES. 



Make sections of young internodes as directed in 1025, secur- 

 ing in every case accurate measurements of all the parts, both 

 before and after their separation. It will be well to examine in 

 like manner a large number of young roots, stems, leaves, and 

 parts of flowers, noting in all cases the age of the part examined. 



XX. INSECTIVOROUS PLANTS. 



In the study of these plants the student is advised to read 

 carefully Mr. Darwin's work on the subject, and verify, by means 



