328 



EXPERIMENTS WITH PLANTS 



bears no leaves, but their work is performed by the 

 green rind of the stem and branches. As compared 

 with the normal plant, the loss of water in per cent of 



its own weight is 

 ver}^ small. Just 

 how much it 

 amounts to we may 

 determine by weigh- 

 ing at intervals , 

 For purposes o f 

 comparison we may 

 cut off a branch of 

 the normal Potato, 

 trim off the lower 

 end until the branch 

 weighs about the 

 samo as the other, 

 and then place it 

 with the cut end in 

 water, over which 

 we pour a little cotton-seed or olive-oil. We now deter- 

 mine loss of weight in the usual way and compare (tests 

 should be made under the same conditions for both) . 



If we take sections of the stem we find that, as 

 compared with a normal plant, the cuticle is thicker, 

 the cells are much smaller, and are very densely filled 

 with starch, i. e., the stem is used as a place for stor- 

 age of food. 



180. The potato at the left grew iu u moist place in 

 dai'kness: the one at the right grew in a dry place 

 iu strong light: both grew for the same length of 

 time. 



