248 



EXPERIMENTS WITH PLANTS 



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

 Wherever the outer surface of the wood is concave, 

 each new layer of wood finds less room to spread out, 

 and hence is obliged to thicken up more and more 

 until a huge buttress may l;o formed beneath a branch, 

 as is shown in Fig. 142a. All concavities thus tend 



to (ill up in time. 

 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 

 also the experiment of slitting the bark with a 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 



142a. 



Buttress formed on the lower side of a branch 

 where it joins the trmik. 



