THE STRUCTURE AND GROWTH OF STEMS 181 



some trees with thin bark, like birch, lenticels permit the 

 cortex to manufacture food throughout the life of the plant. 



/. Grafting and Budding. - In the culture of fruit trees 

 it was long ago found to be very desirable to join different 

 parts of different plants together and thus form one in- 

 dividual. Some apple trees have strong and hardy roots 

 and stems and leaves ; their nutritive organs are excellent 

 for the purposes of apple culture, but the fruit which they 

 bear is small and sour. Other apple trees, which bear 

 delicious fruit, are rather weak and not hardy as to their 

 vegetative organs. So, long ago, fruit growers experi- 

 mented, trying to get twigs which bore good fruit to grow 

 upon stems which were hardy. They were successful in 

 their experiments. They perfected a process by which 

 many kinds of fruit besides apple are now cultivated. The 

 name of that process is grafting. It is a process which is 

 based upon the activity of the cambium layer. 



The hardy plant whose roots are in the ground, and upon 

 which the graft is to be made, is called the stock. The 

 twig which is to be made to grow upon the stock is called 

 the scion. The scions are usually cut in the fall, kept in 

 moist soil or sand, and grafted in the spring. Thus they 

 are cut when their resting period has begun, and grafted 

 just when their activity is about to begin again ; these 

 times of cutting and grafting have been found to be most 

 favorable for securing successful results from the operation. 

 When the graft is made, the cambium of the scion and the 

 cambium of the stock are brought into close contact, and, 

 if both are active, they grow together. The stock and 

 scion soon become as closely related as the stock and its 

 natural branches. Just before grafting, the ends of the 



