12 CHAP. II. HIGH MAGNIFICATION CRESCOGRAPH 



may even be missing. The difficulty is obviated by accurate 

 adjustment of the plate in a vertical plane by means of 

 regulating screws. 



Experimental Accessories 



The soil in a flower-pot is liable to be disturbed by 

 irrigation and the record be consequently vitiated. This is 

 obviated by wrapping the root, imbedded in a small quantity 

 of soil, in a piece of cloth, the lower end of the plant being 

 held securely by the clamp of the plant-holder. In order 

 to subject the plant to the action of gases and vapours, 

 or to variation of temperature, it is enclosed in a cylindrical 

 chamber constructed of a sheet of mica, with an inlet and 

 an outlet pipe. The chamber is maintained in a humid 

 condition by means of a sponge soaked in water. Vapours 

 and gases can be easily introduced or removed from the 

 plant-chamber ; variation of temperature is simply effected 

 by blowing in heated or cooled water-vapour. 



Any quickly growing organ of a plant will be found 

 suitable for the following experiments ; complications 

 arising from circumnutation may be avoided by employing 

 either radial organs, such as flower peduncles, buds, or the 

 pistils of certain fiowTrs, or the hmp leaves of various 

 species of grass. It is advisable to select specimens in 

 which the growth is fairly uniform. I append a repre- 

 sentative list of different specimens in which, under favour- 

 able conditions of season and temperature, the rates of 

 growth may be as high as those given below : 



Table I. — Average Rate of Growth ix Different 



Specimens. 



Peduncle of Zephyranthes 

 Leaf of grass 

 Pistil of Hibiscus flower 

 Seedling of Wheat 

 Flower-bud of Crinum 

 Seedling of Scirpus Kysoov 



o- 7 mm. per hour 

 I • lO 

 I -20 



1 -Go 



2 -20 



3-00 



The specimen employed for experiment may be an 

 entire plant ; it is, however, more convenient to employ 



