CARBOHYDRATES 65 



ture of C., and ceases at 7, or above. Also, if potatoes in which 

 the maximum amount of sugar is present (not over one-sixth 

 of the total starch can be converted into sugar) are exposed to a 

 higher temperature the sugar soon disappears. 



In general, however, it may be said that each particular species 

 of plant has its own particular preference for a specific carbohy- 

 drate as its reserve food material, and elaborates the proper enzymes 

 to make it possible to utilize this particular carbohydrate for its 

 metabolic needs. 



Again, the question as to whether the storage of energy- 

 producing materials for the use of the next generation shall be in 

 the form of carbohydrates or of fats seems to be definitely con- 

 nected with the size of the seed, and the consequent available 

 storage space (see page 138). Animals habitually use the space- 

 conserving form of fats for their energy-storage, while plants more 

 commonly use carbohydrates for this purpose, except in the case 

 of those small seeds in which sufficient energy cannot be stored in 

 carbohydrate form to develop the young seedling to the point where 

 it can manufacture its own food. As a general rule, nuts, which 

 contain the embryo of slow-growing seedlings, and need large 

 proportions of energy reserve, are characteristically oily instead 

 of starchy in type. 



But, aside from temperature reactions and space requirements, 

 there is no law which has yet been discovered which determines the 

 character of the energy-storage compound which any given species 

 of plant will elaborate. The process of photosynthesis would 

 seem to be identical in all cases, at least up to the point of the 

 production of the first hexose sugar; but the transformation of 

 glucose into other monosaccharides, disaccharides, and polysac- 

 charides seems to be a matter which obeys no rule or law. 



Finally, there remains to be considered the occurrence and 

 uses of sugars in the fleshy tissues of fruits. These tissues have, 

 of course, no direct function in the life history of the plant. They 

 surround the seed, but they must decay or be destroyed before the 

 seed can come into the proper environment for germination and 

 growth. In most fruits, starch is the form in which the carbo- 

 hydrate material is first deposited in the green tissue, but as the 

 fruit ripens the starch rapidly changes into sugars, with the result 

 that the fruit takes on a flavor which makes it much more attractive 

 as a food for men and animals. This purely biological significance 



