202 TEXTBOOK OF PLANT PHYSIOLOGY 



ingly does external environment affect the proteins in seeds. The 

 drier the climate, the higher is the protein content in wheat grains. 

 According to investigations by the Institute of Applied Botany 

 in Leningrad, the same wheat, when grown in the Province of 

 Smolensk (western Russia), gave grain with 10.9 per cent protein; 

 in the Province of Kostroma (central Russia), 13.6 per cent; and in 

 eastern Siberia, 18.2 per cent. Similarly, the nature of the soil 

 exerts an influence upon the composition of the grain. Soils some- 

 what alkaline and with a low water-supplying power will likewise 

 increase the protein content of the grain. The dry climate and the 

 alkalinity of the soil of the southeast of Russia, therefore, while 

 making harvests uncertain in this region, still impart to wheat a 

 very high quality. The quantitative and the qualitative compo- 

 sition of fats in oily plants likewise depend upon climate. A dry 

 and hot climate as a rule, makes seeds of the sunflower more oily 

 and increases the relative quantity of the unsaturated fatty acids 

 in the oil obtained from them. 



66. Types of Reserve Carbohydrates. Their Products of 

 Hydrolysis. — Of the many groups of carbohydrates, seeds contain 

 mostly starch, a polysaccharide insoluble in water and of the empir- 

 ical formula Cr.HioOs. During the maturation of seeds, starch is 

 formed in the leucoplasts of the reserve parenchyma, composing 

 the main mass of the endosperm or of the cotyledons. It is present 

 in the form of particles or grains of various shapes and sizes, each 

 characteristic of certain species of plants. Hence, under the 

 microscope, it is possible to determine from the structure of the 

 grains to what kind of plants the starch may belong. This is one 

 of the most important methods of recognizing and distinguishing 

 admixtures in flour. In their detailed structure, starch grains are 

 sphaerocrystals, composed of very fine, closely associated and 

 radially arranged crystalline needles. 



The formula C0H10O5 does not express the exact composition 

 of starch. All the methods of determining the molecular weight 

 have disclosed that the starch molecule is very large, and that the 

 formula should be written (CoHioOs),,. The cryoscopic method of 

 determination has given an especially large size to the molecule. 

 Various authors have suggested different values for n ranging from 

 30 to 638. 



Being a polysaccharide, starch readily changes into sugar. 

 Upon the action of dilute acids it produces glucose. The starch 



