13 PLANT PHYSIOLOGY. 



EXPERIMENT 58. This may be tested by so arranging roots 

 growing geotropically downwards that they will be deflected if sen- 

 sitive to a moist surface placed near them. Prepare a moisture- 

 cylinder as follows. Take two thoroughly cleaned (and preferably 

 sterilized) Zurich germinators ; soak them a few minutes in water; 

 then, holding them under water, run a broad rubber band around 



FIG. 35. ARRANGEMENTS FOR THE STUDY OF HYDROTROPISM. 



One-third the true size. 



their junction. They may now be lifted from the water and they 

 will remain full ; a wire is placed around them as in Fig. 35 to pre- 

 vent their coming apart and to form a support by which they may- 

 be suspended in a darkened bell-jar. Take now seeds of beans, corn, 

 oats (or others in which the hypocotyl does not lengthen) which 

 have been germinated in sphagnum to a cm. radicle, and attach them 

 by slender rubber bands to the germinators, as shown in Fig. 35 

 with the radicles touching the moist surface. The cylinder is then 

 to be suspended in a bell-jar, covered from the light, and placed in 

 a favorable growth temperature. The bell- ; ,ar is not, however, to 

 be tightly closed (for thus a saturated atmosphere would result in 

 which the roots would grow vertically downwards) : the stopper of 

 the jar should be left out, and the rim raised a cm. or less from the 

 table. Observe the growth of the roots and stems. What is the 

 difference in the hydrotropism of roots and of stems ? 

 Mustard-seeds may be used (Fig. 35, right) without preliminary 

 germination ; their mucilage attaches them sufficiently to the cylinder, 

 Doubtless small flower-pots (with the holes stopped with corks) could 

 be used as well as the germinators. It is not indispensable to use the 

 rubber bands, for if the germinators are filled with sphagnum, as wet as 



