GROWTH 



177 



called circumnutation, make ifc seem absolutely necessary to 

 experiment upon small plants indoors; but when this is 

 done, other complications ensue, such as are due to watering 

 the soil and its subsequent drying, the jarring of the meas- 

 uring instruments, etc., etc. Furthermore, not all plants 

 grow in straight lines. The tips of the stems of many are 

 sooner or later so curved that the length of these parts can 

 only be estimated. To overcome these various difficulties 

 many instruments have been devised. From the direct ob- 

 servation and measurement of small organisms or parts by 

 means of microscopes, vertical or horizontal, to the com- 

 plicated self-recording auxanometers of the well-equipped 

 physiological laboratory, the utmost variety in methods 

 and means exists. Illustrated descriptions of instruments 

 are so accessible that space need not be taken here for 

 them.* Most of these instruments are but modifications 

 and improvements of those invented by the masters in 

 plant-physiology, especially by Sachs. The principle of all 

 is to magnify the growth so that the evidence or the record 

 of it is visible. The need of this is made evident by the 

 following figures 



* See Ganong. in Botanical Gazette, vol. XXVII., 1-899. 



Arthur, XXII., 1896. 



Stone, XXII., 1896. 



Golden, XIX., 1894. 



Frost, ' Minn. Bot. Studies, " XVII.. 1894. 



f True. R. H.. in Annals of Botany, vol. IX.. p. 371, 1895. Figures in 

 Table I give this average. 



i Kraus G.. in Annales du Jardin Botanique de Buitenzorg, vol. XII.. 1895. 

 Askenasy. in Verhandl. d. naturh- med. Vereins in Heidelberg, 1879. 



* Hofmeister, in Jahreshefte d. Vereins f. Vaterl. Naturkunde in Wurttem- 

 berg, 1874. 



H Brefeld. Untersuchungen iiber Schimmelpilze. Heft 3. 1877. 



