2O4 



THE TEACHING BOTANIST 



Experiment No. 6. Place two simi- 

 lar plants in bell-jars having ground- 

 glass bottoms, which can be sealed 

 with vaseline to ground-glass plates, 

 as in Fig. 19. In the saucer in one 

 and in the tube in its cork place soda- 

 lime (an absorber of C(X), and in the 

 other place simply sawdust, in order to 

 have all conditions alike in both ex- 

 cept for the absence of CO 2 , and its 

 presence, respectively. After about two 

 days' exposure to bright light, the 

 application of the iodine test to leaves 



FIG. 19. - Apparatus for wiR ghow nQ gtarch in those with soda _ 

 study of need of carbon 



dioxide in photosynthe- lime, and abundance in the other, proving 

 sis - x 5- that CO 2 is essential to photosynthesis. 



VIII. Special Morphology and Ecology of Shoot 



and Root 



The plasticity of root and shoot (leaf and stem) in 

 form and structure is far greater than is shown by 

 the examples studied by you under Exercise 28, and 

 even allows of their modification into special new 

 organs for carrying on new functions ; to this end 

 they may be so altered in shape, size, color and texture, 

 as to disguise completely their original nature. Their 

 positions relative to one another in the plant usually 

 remain unchanged, however, and this forms the best 

 guide to the identity of the disguised parts. 



