VALUE OF CORK 85 



weigh both again the next day, and the next. The 

 peeled potato loses weight at once, and will shrink 

 very much in size. 



In an experiment made in this way the two potatoes 

 each weighed f tola. One was peeled, and in two 

 days (in a cool place) it had lost \ tola ; and in 

 another two days had decreased by yet another J tola ; 

 while the difference in the other was hardly visible. 

 Three days later the peeled potato weighed scarcely 

 an eighth of a tola and had shrunk to less than a quar- 

 ter of its original size, while the other was hardly, if at 

 all, different. 



5. By the formation of cork and bark from the 

 cambium, plants are able to heal over wounds caused 

 by the breaking of branches by wind or animals. Thus 

 it is that neat rounded lumps grow where branches 

 have been cut off close to the stem. But if a 

 portion of the branch is left, so that the exposed sur- 

 face is not close enough to the main axis to be 

 well supplied with sap, the phellogen gets dry and 

 dies, and very soon the core of the branch, exposed 

 as it is to rain and attacks of insects and fungi, be- 

 comes rotten and hollow. In time the rot may extend 

 into the trunk of the tree till at last the whole is 

 destroyed, or the weakened trunk breaks across in a 

 high wind. Many a tree has died for no other reason 

 than that a branch had been broken off carelessly, 

 so that the phellogen could not form and cover the 

 wound, instead of being cut off as close as possible to 

 the stem to allow the natural healing to take place. 



6. In section 2 we learnt that one great difference 

 between monocotyledons and dicotyledons is that the 



