198 



PLANT PHYSIOLOGY 



The foregoing experiments will show very clearly where 

 growth is most active in typical leaves, roots, and stems. From 

 this basis the student should extend his knowledge, by addi- 

 tional experiments upon other organs if practicable, and by 

 study of books in any case, until he gains so clear an idea of the 

 distribution of growth that he can construct a diagram to show 

 its distribution and relative intensities throughout a typical com- 

 plete higher plant. 



C 



ill 



Fig. 53 (upper). Space-marking wheel; Xi- 

 The rim is a rubber stamp marked with plain cross lines 2 mm. apart. 



Fig. 54 (lower). Space-marking disc; XI- 



It consists of a rubber stamp marked in squares 2 mm. on a side, connected by a 



spring handle with a felt-covered disc. 



It is essential rffxt to determine how rapid this growth may 

 be, which presents the experimental problem: 



What is the rate of growth of leaves, roots, and stems under 

 ordinary conditions? 



This may be determined by direct measurements, at definite time- 

 intervals, with fine rulers or calipers; but most growth is so slow 

 that in practice it is advantageous to make use of magnifying arrange- 

 ments, which may be arranged not only to exhibit growth (auxoscopes), 

 but also to measure (auxanometers), and even to record it (auxo- 

 graphs). In any case it is best to begin the study with a structure 

 of rapid growth and easy manipulation. 



Experiment. Select a stem of rapid vertical growth (e.g., a flower- 

 stalk of Grape Hyacinth or other bulbous plant); when it has just 

 appeared above ground, arrange it for study by aid of an auxa- 

 nometer, or, better, by an auxograph; give favorable conditions for 



