330 



The Living Plant 



ing off thereon the precise growth, magnified of 

 course proportionally throughout. The papers can 

 then be removed from the cylinders and joined end 

 to end in a continuous roll, or else a flat band. Thus 

 is a plant made to write its own record of growth in 

 a way convenient for scientific use. Such a record, 

 obtained b}^ one of my own students, and showing the 

 growth of the flower-stalk of a Grape Hyacinth from 

 its first appearance above ground to the completion 

 of flowering, is shown, greatly reduced of course, in 

 the accompanying illustration (figure 122). And 

 by suitable modifications of the same auxograph (for 

 so it is called because it is a growth writer), the 

 growth of roots, leaves and other parts can likewise 

 be registered. 



A growth record like that of our figure is very ex- 

 pressive, but the facts can be brought out still better 

 in the form of a graph like that which already has 

 been used and described under Transpiration; and 

 such a graph is presented in our figure 123. The 

 base line is laid off in divisions of time, each space 

 representing one hour, while the vertical lines are 

 marked off with the number of millimeters of growth 

 (magnified) per one-hour period, these marks being 

 joined by straight lines in the usual way. In the 

 resulting polygon, as the reader can see, the rise and 

 fall of the lines corresponds to the rise and fall in the 

 rate of growth. The reader must remember that such 

 a graph represents the rate of the growth, not its 

 amount, which fact explains the feature, puzzling 

 to some people, that a growth graph can fall as well 



Fig. 122.— Pho- aS riSe. 

 tograph, re- 

 duced to one-tenth the true size, of the record papers taken from the cylinder of the 

 auxograph (of figure 121) during the growth of a flower-stalk of Grape Hyacinth. 

 The heavier cross lines indicate noon of each day. 



