60 Plant Physiology 



next period ; otherwise dry in any oven used for dry steriliza- 

 tion during two successive laboratory periods), weigh, and 

 record. If not weighed immediately, leave the material in a 

 desiccator over fresh (dry) CaCl2 until determined. Calculate 

 percentage of water. 



Determine the water-holding capacity of any rich garden 

 loam, sand, and powdered quartz which may be available for 

 later experiments. To completely saturate the material a sim- 

 ple method is to fill a small pot or wire basket with the moist 

 material, tamp down lightly, dip into (or pour on) water care- 

 fully until slightly more than saturated ; then, as soon as the 

 drip has ceased, dump approximately the quantity desired into 

 the weighed vessel, and proceed as before. In calculating the 

 water-content of soils it is to be remembered that at present 

 the method more commonly employed is to determine the ratio 

 or percentage of water, with respect to dry weight of soil, a 



"w w 

 calculation easily made as follows : r = j l , in which w - 



w w 



weight of saturated soil and vessel ; w', of dry soil and vessel ; 

 w", of vessel ; r bsing the per cent of water. 



Root-systems. - - The distribution of roots in the soil may 

 be studied by careful excavation and washing out (cf. Ten 

 Eyck, Kansas Agl. Exp. Sta. Bui. 127). A far better concep- 

 tion of the fine root-system (under fairly natural conditions only 

 when care is taken in the manipulation) may be obtained for 

 demonstration, according to the method of Rotmistrov, by 

 growing plants in flat zinc, or zinc-lined, boxes which for class 

 purposes are large enough if 1 inch across, about 15 to 18 

 inches wide, and 18 inches deep. The box should contain sur- 

 face-soil and sub-soil well compacted and arranged as in 

 some local soil type. During the period of growth the boxes 

 should be immersed to the surface in deep boxes of sand or soil. 

 Grow r th should be permitted to proceed for a month or more. 

 When the boxes are open, a side is removed, a fine mesh wire 

 screen (about k inch) is laid on the soil, the whole being inverted ; 

 the soil is left upon the screen, and upon dipping this gradually 

 into water an almost perfect root-system may be obtained. 



