216 GROWTH OF STEMS 
line which it makes on the paper carried around on a revolving 
drum. (Fig. 197.) Such an apparatus has the advantage in that 
one can see just how growth proceeds at any period during day or 
night, if the apparatus is so manipulated that the hour at which 
any part of the line is made can be determined. Measurements 
by such an apparatus show that the rate of growth of an organ 
is not uniform, but, beginning slowly, it gradually rises to a point 
where growth is most rapid and then gradually falls away, finally 
Fig, 197. — Auxanometer in operation. As the plant elongates, the small 
pulley (w) revolves, revolving with it the large pulley (r) which magnifies 
the motion and transmits it to the marker (z) that marks on the drum (1). 
The drum is revolved by the apparatus (k) at its base and this apparatus 
is connected with the clock (w). After Pfeffer. 
ceasing as the organ approaches maturity. This mode of enlarg- 
ing, which is commonly known as the grand period, is character- 
istic not only of stems, but also of fruits, flowers, leaves, and roots. 
The fundamental cause of the grand period in any organ is due to 
the fact that cells themselves enlarge in this way. Unlike leaves, 
flowers, and fruit where the expansion is quite even throughout, 
stems expand by each internode going through its grand period 
independently of the other internodes. Thus between the upper 
internodes in which the grand period is just beginning and those 
