4OO APPENDIX. 



33. To show the effect of gravity as a stimulus on growing regions 

 of tipright leaves and stems. (HIT 287-290.) 



A. Support an onion, roots down, in a vessel of water so that 

 it is half immersed, until the leaves are about 10 cm. long. Then 

 turn it so that leaves are horizontal and observe where curvature 

 occurs. 



B. Cover the bottom of a deep dish about 25 cm. long with a 

 layer of wet sand, and bank this against one end to the top. Into 

 this bank stick horizontally several grass stems having at least 

 one node ; cover with a glass plate. After 24-48 hours observe 

 curvature. Cut a longitudinal section of the node and observe 

 the part of the leaf-sheath in this curvature. 



34. To show the effect of direction of light as a stimulus on leaves. 



(IF 285.) 



Set a potted plant (geranium, sunflower, nasturtium, or mallow) 

 in the dark for 24 hours ; then place it before a window, shading 

 it so that light reaches it chiefly from one direction. Mark certain 

 leaves and record the position of the plane of the blade ; 24 hours 

 later observe the position and compare with first. 



35. To show effect of direction of light as a stimiilus upon stems 

 and roots. (^ 285.) 



Grow seedlings of white mustard thus : Tie loosely over the 

 mouth of a jelly-glass a double piece of fine bobbinnet; fill vessel 

 with tap water to the net, on which place seeds ; set in dark, re- 

 placing water as it evaporates, until seedlings are 3 cm. high, 

 with roots as long or longer. Then place in a box, blackened 

 inside, into which light is admitted, through a hole 4-5 cm. 

 in diameter, at right angles to stems and roots. Observe curva- 

 tures 24 hours later. 



36. To show effect of intensity of light as a stimulus on certain, 

 leaves. (^[ 297.) 



Observe the position of the leaflets of white, red, or sweet 

 clover, bean, locust, or oxalis at 3 P.M., 6 P.M., at dusk (or after 

 nightfall by using a lantern) and at 8 A.M. In the morning darken 

 with a box a plant showing these movements. After an hour or 

 two, observe the position of leaflets. 



37. To show effect of contact as a stimulus to tendrils. (^ 293.) 

 Stroke with a pencil the concave side of the tip of a tendril of 



passion vine, squash, wild cucumber, or balsam-apple, on a warm 

 day or in a hothouse, and observe curvature which follows in a 

 few minutes. 



