COURSE OF GROWTH 287 



the axial or radial dimension, or of the increase in weight. In- 

 crease in thickness of most organs is due to the direct activity of 

 the generative layer, the development, and expansion of the tissues 

 formed, and is very minute and difficult to estimate. Such 

 growth has been found to follow the same laws as that exhibited 

 by the elongation^of the axis. 1 Measurement of the elongation 

 of an organ through any considerable portion of the period during 

 which it is passing from the rudimentary stage to maturity, af- 

 fords an opportunity for determination of the rhythmic action of 

 protoplasm, and also of analyzing the influence of various factors 

 on the process. The best method for the measurement of 

 growth consists of the use of some instrument in which the tip of 

 an organ, which is being pushed forward during growth, is attached 

 to the short arm of a lever, the tip of the longer end of which, 

 carrying a pen traces a line on a cylinder actuated by a clock- 

 work. If the growth of the plant is as much as a centimeter daily 

 the simple lever auxanometer shown in Fig. 137 will be found 

 best, though many other good forms have been described and may 

 be easily set up. 2 For the measurement of lesser increases, an in- 

 strument with a compound lever will be necessary if a proper 

 analysis of the results is desired. Estimations of accretions in 

 weight may be made by some form of continously registering, or 

 recording balance. 



1 Frost, W. D. On a new electrical auxanometer, and continuous recorder. 

 Minn. Bot. Stud. 1 : 181. 1894. 



Golden, K. E. An auxanometer for the registration of the growth of stems in 

 thickness. Bot. Gazette. 19: 113. 1893. 



2 Arthur, J. C. Laboratory apparatus in vegetable physiology. Bot. Gazette. 22 : 

 463. 1896. 



Barnes, C. R. A registering auxanometer. Bot. Gazette. 12: 150. 1887. 



Bumpus, H. C. A simple and inexpensive auxanometer. Bot. Gazette. 12 : 149. 

 1887. 



Corbett, L. C. A device for measuring plant growth. W. Va. Exp. Sta. 9th 

 Ann. Report. 236. 1896. Also, An improved auxanometer and some of its uses. 

 W. Va. Exp. Sta. 12th Ann. Report. 1900. 



Ganong, W. F. Some appliances for the elementary study of plant physiology. 

 Bot. Gazette. 27 : 255. 1899. 



Stone, G. E. Botanical appliances. Bot. Gazette. 22 : 258. 1896. 



