GROWTH 151 



456. Whj^ does the bark of a tree never become as thick as the wood? 



457. If you were to determine the age of a tree by counting the annual 

 rings, where in the tree would you make the count? Why? 



458. In a cut stump, the rings are usually wider next the pith than 

 they are far out in the trunk. Why? 



459. How can we use the annual rings of old tree trunks to study 

 past climatic conditions? What cautions must we observe in doing so? 



Note. — In grafting, a small twig (the scio7i) which has been cut from 

 one plant is placed in close contact with a branch of another plant 

 (the stock). This may be done in several ways, but in all cases the 

 tissues of the stock and scion are both cut open and so placed together 

 that the cambium of one touches the cambium of the other. If the 

 operation is successfully performed, the stock and scion will unite and 

 the latter will grow out as a branch of the former. 



460. In the process of grafting, why is it necessary for the cambial 

 layers of stock and scion to be in close contact? 



461. After a graft has been successfully made, how does water get 

 from the tissues of the stock into those of the scion? 



462. Why is it important to use a very sharp knife in grafting 

 operations? 



463. In grafting, why is it necessary to cover the cut surfaces with wax 

 or a similar substance? 



464. Plants which are not rather closely related to one another 

 cannot be grafted together. What explanation can you suggest for 

 this fact? 



465. Monocotyledonous plants can almost never be grafted. Why? 



466. Nurserymen sometimes slit the bark lengthwise on strong and 

 rapidly growing stems to hasten the production of new wood. Why 

 does this practice aid in producing the desired result? 



Note. — Pruning is the process by which certain twigs or branches 

 are removed from cultivated trees in order to attain some desired result. 



467. Why does careful pruning make a tree more vigorous and 

 healthy? 



468. Why is pruning generally done in spring, fall or winter rather 

 than in summer? 



469. How differently would you prune a tree if you desired fruit 

 production from the way you would prune it if you desired the produc- 

 tion of timber? 



