1248 



EXPEBIMENTS WITB PLANTS 



opposite sides by the bending of the tree in the wind. 

 The buttresses (Fig. 142a) below large branches are 

 probably due to the sinking of the branch under the 

 weight of foliage, thus loosening the bark below and 

 allowing the wood to expand, while above the branches 

 the reverse is the case. Experiments may be made to 



test the effect of 

 "binding" on the 

 growth of the 

 wood by wrap- 

 ping a branch 

 securely with 

 wire during the 

 growing season 

 and investigating 

 it at the close of 

 the season. Try 

 the bark with a 



Buttress formed on the lower side of a branch 

 where it joins the truti'k. 



also the experiment of slitting 

 knife. 



The growth of the cambium adds each year a layer 

 to the bark, as well as to the wood, so that although 

 the bark continually wears off on the outside it grows 

 thicker each year as the tree grows older. (The stems 

 of Monocotyledons have no cambium and do not grow 

 thicker from year to year.) 



It is by means of the growth of the cambium that 

 the scion and stock unite in grafting. Find out what 

 you can about this. Make sections through the place 



