n8 



PLANT PHYSIOLOGY. 



79. Is the direction of growth of primary root and primary 

 stem guided by internal or by external influences ? 

 Answer from Experiments 44 and 45. 



EXPERIMENT 44. This may be tested for roots, by planting a 

 number of seeds in as different positions as possible, and observing 

 the positions the roots take in issuing from them. Near the top of 

 a germination-box (Fig. 30) filled with sphagnum, plant five or six 

 soaked horse-beans in as different positions as possible. Keep the 

 whole dark and moist and observe positions taken by the roots. 

 Another excellent method is the following. Prepare a moist dark- 

 chamber thus : Select a five-inch (or larger) flower-pot and drill out the 

 bottom (easily done with a hammer and screw-driver), in place of 

 which a cork is to be fitted (Fig. 31). Pin to this five or six seeds in 



FIG. 31. MOIST-CHAMBERS FOR GEOTROPIC EXPERIMENTS. 

 One-fourth the true size. 



different positions and bring them out to the heads of the pins ; sur- 

 round them with sphagnum kept wet; place the cork in the pot and in- 

 vert the latter in a saucer of water. The roots grow excellently in such 

 a moist-chamber. After the roots have attained a length of 2 or 3 cm. 

 invert the cork under another pot, and observe effect upon the roots. A 

 flower-pot stood in a dish of water makes the best of moist-chambers. 



An ordinary funnel to supply the sloping glass surface is a fair 

 substitute for the germination-box. 



In all such experiments it is necessary to use a seed in which the 

 hypocotyl does not elongate and raise the cotyledons ; hence horse- 

 beans or corn are very good. 



