CHARACTER AND RATE OF GROWTH IN STEMS 215 



less it is so slow, except in a few cases, that it is imperceptible 

 to the unaided eye; and, therefore, to directly observe it, the 

 growing organ must be watched under the microscope. How- 

 ever, in measuring growth in large organs, such as stems, leaves, 

 and roots, other methods that are more convenient are usually 

 employed. Thus by marking a stem into segments as shown 



FIG. 196. Stem of a seedling marked to show the regions of most elongation. 

 A, stem just after marking. B, stem after a few hours growth. 



in Figure 196 and observing the spread of the marks apart, 

 one can easily determine what part of the stem is most active 

 in elongation. Special kinds of apparatus run by clockwork, 

 one of which is known as the auxograph (meaning "growth 

 writer") and another as auxanometer (meaning "growth meas- 

 urer"), have been so devised that the rate and fluctuations 

 in growth are recorded by a pen which indicates the character of 

 the growth throughout a considerable period by curvatures in the 



