2 22 THE PHYSIOLOGY OF PLANTS 



we cannot at present base our answers on precise experiments, 

 but we must make use of general experience, which has been 

 accumulated during years, or indeed centuries, of horticultural 

 practice. Science has yet to make many investigations into 

 such practical subjects. 



In all cases in which the horticultural value of a cultivated 

 plant lies in its flowers, or in the resulting product of those 

 flowers, the fruit, it is desirable to increase as much as possible 

 the number of flowering buds. On this point we know by 

 experience that plants will only develop flowering buds when 

 the food material formed in the leaves is copiously stored up in 

 the stem and branches as reserve material, and not when this 

 material is immediately used up in the production of new 

 vegetative organs (leaves). 



In horticultural practice it is common to observe in the 

 case of perennial plants that a continuous and excessive for- 

 mation of leaves is detrimental to the production of flowers 

 (pine-apple and vine growing). Of our apple-trees it is well 

 known that in warm insular climates they grow into magnifi- 

 cent foliage trees, but remain unproductive of fruit. Growers 

 of cactuses will have found out that if the plants are copi- 

 ously watered during the winter in a warm house or room, they 

 will very rapidly produce new shoots, but no flowers. Many 

 Australian plants (Metrosideros, Cantua dependens, Correa) are 

 generally kept in small pots by gardeners because they are 

 said to blossom better. 



In all these cases it proves to be advantageous to prevent 

 the development of shoots and to bring about a complete 

 period of rest. The best means of doing this is by drought, 

 and under certain circumstances by diminution of the tem- 

 perature. We have already touched upon another method of 

 attaining the retention and storing up of food material by 

 ringing and notching the branches. 



That a diminution of the supply of water accompanies the 

 production of flowers in nature may be gathered from the fact 

 that most trees and shrubs produce their flowers on short re- 

 duced shoots or spurs. The comparison of the anatomical 

 structure of such a short shoot with that of a long leafy shoot 

 confirms our statement, too, that an increase in stored food 



