CHAPTEK XV 



THE STORAGE OF FOOD-BESEBVES— ECONOMIC BOTANY 



Plants differ from animals in many ways. We have 

 drawn attention to some. In the matter of the storage of 

 food-reserve we have another. Animals rarely store up 

 food in their own bodies for future use ; to some extent 

 hibernating animals do, and there is the remarkable case 

 of the fat-tailed sheep of Thibet which store up fat in their 

 tails. Plants, on the other hand, by the very nature of 

 their economy, are compelled to make and store up food 

 in preparation for periods when a great demand for 

 nourishment is made. Most plants have to make pro- 

 vision for the formation of flowers and seeds. For this a 

 largo amount of food-material is required in a very short 

 time, and in many plants the whole of their vegetative 

 activities seems to be a preparation for this function. 

 The annual, for example, accumulates reserves until 

 flowering, when a migration of food-material takes place 

 from all parts of the plant towards the flowers ; the food- 

 material, elaborated by the parent, passes into the seeds, 

 and the drain is so exhausting that the plant dies. Her- 

 baceous perennials prepare for the winter by storing up 

 reserves of food in their perennial parts underground — 

 e.g., in bulbs, rhizomes, tubers, etc. When spring comes, 

 a current of food-material pours from the seats of storage 

 towards the opening buds, and is utilized for the rapid 

 growth of the aerial shoots and leaves. Trees also accu- 

 mulate great reserves of food.- When the buds open in 

 the spring, the demand for nourishment is very great, and 

 the ascending stream of watery sap, enriched with food- 

 material drawn from the stores of reserve, passes into the 

 unfolding leaves. 



The most common form of food-reserve is starch. 

 The ceUs of the potato are fiUed with grains of starch ; 



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