HORTICULTURE A GREAT GREEN CARPET 433 



tary a topic as the carbohydrate-nitrogen relationship and one which, from 

 the standpoint of the scientist, may properly be called naive. 



Simply stated, nitrogen is secured by the plant principally from the soil and 

 is influenced in amount and availability by temperature, soil moisture, root 

 penetration, and other soil environmental factors. On the other hand, the 

 carbohydrates are manufactured in the green portion of the plant from the 

 carbon dioxide of the atmosphere in the presence of light. The general idea 

 is that the ability of a plant to fruit is indicated by the relationship between 

 carbohydrates and nitrogen in the plant. 



On this basis, fruit trees may be placed in one of four classes as regards 

 C-N relationship and fruiting: 



Class I is the plant which has an abundance of nitrogen but a deficiency 

 of accumulated carbohydrates. It is the thin-wooded, spindly, weak tree that 

 grows in the shade. It is like an undernourished child. It does not develop 

 and does not fruit. 



Class II is the adolescent, which, supplied with an abundance of both 

 nitrogen and carbohydrates, keeps on growing exuberantly, with large dark 

 green foliage, but does not get down to the business of fruiting. 



Class III is the highly productive individual, in which sufficient reserve 

 carbohydrates have accumulated to provide for fruit-bud formation and 

 fruiting. This is the age of maximum production and the joy of the successful 

 fruit grower. 



Class IV is the age of senescence and decline, where carbohydrates have 

 accumulated to such a degree that the foliage is yellowish in color, the tree 

 biennial in bearing, and the characteristics of age appearing — not unlike the 

 man who accumulated sufficient avoirdupois to be termed "a bit heavy" or 

 even "corpulent," and who is content to sit by the fire in his slippers, except 

 for sporadic outbursts of enthusiasm from time to time which slowly diminish. 



With these four classes clearly in mind, it has been shown that much can 

 be done in the fruit plantation to control the behavior of a tree. The weak 

 tree of Class I needs to be brought into the sunshine, where it may manu- 

 facture more carbohydrates, pass into the adolescent stage of Class II, and 

 there accumulate a sufficiency of carbohydrates to settle down into the 

 productive period of middle life (Class III). Conversely, the aging tree of 

 Class IV can be rejuvenated and brought back into the productivity of 

 Class III both by severe pruning, which removes excess carbohydrates, and 

 by application of nitrogenous fertilizers, which increase the nitrogen balance. 



Further, ringing and girdling are helpful in bringing a tree from Class II 

 of adolescence over into the productive Class III by virtue of the fact that 

 carbohydrates are induced to accumulate above the ring or girdle. Root 

 pruning is similarly helpful, but for the reason that it reduces the intake of 

 nitrogen. High summer temperatures may delay fruiting in young trees 

 because the tree respires carbohydrates too rapidly to accumulate a sufficient 



