216 



AGRONOMY 



young twigs. The habit of cutting off the useless flowers after 

 blooming may also be regarded as a form of self-pruning, as is 

 the casting of the leaves in autumn. It is commonly supposed 

 that only flowers that fail to be pollinated are cut off by the 

 plant, but many young fruits are also severed from the branches, 

 otherwise the plant could not make sufficient food for all, and 

 even if it could, the load would be more 

 than it could bear. The advantages to 

 be derived from thinning the fruit on 

 trees heavily loaded is obvious. 



Time to prune. An old rule for 

 pruning is, " Prune when the knife is 

 sharp," indicating that when a plant 

 needs pruning one time is as good as 

 another, but such a rule has many ex- 

 ceptions. The time for pruning any 

 plant depends somewhat upon the time 

 at which it produces its flowers. Plants 

 that form their flower buds in autumn 

 should not be pruned in winter, as this 

 would remove the embryo flowers and 

 fruits. Such plants should be pruned 

 in spring and summer, shortly after 

 they have fruited and before new flower 

 buds have been formed. On the other 

 hand, many plants produce their flowers 

 on the new wood, that is, on twigs produced from winter buds. 

 These may be pruned in winter, since new and vigorous wood 

 will usually be more floriferous than older twigs. In general, 

 winter pruning increases the amount of wood formed and sum- 

 mer pruning induces flowering. Summer pruning has the ad- 

 vantage over winter pruning in that one may then see how 

 the crown of foliage ,is displayed and may more readily 

 remove branches that shade others. Moreover, the cambium, 



FIG. 157. A common form 

 of pruning shears 



