180 FUNDAMENTALS OF FRUIT PRODUCTION 



Relation to Pigment Formation, — A supply of carbohydrates is necessary for 

 the development of certain pigments in leaves, flowers and fruits. Laurent^^*^ 

 showed that fruit pigments are of two types ; some develop only as a result of 

 direct exposure to light; others do not require direct illumination of the fruit 

 but for their development the leaves must be able to manufacture carbohydrates 

 and the connection between the leaves and the fruit must not be interrupted. 

 Kraus^^^ suggests that pigments of both sorts occur in apples. The effect of 

 low temperature or parasitic attack in increasing the pigmentation of fruit or 

 leaves is attributed to an attendant accumulation of sugars, especially glucose, 

 fructose and sucrose. 



Summary. — The elaborated plant foods used in tissue building are 

 manufactured from the nutrient materials obtained from the soil and air 

 at a rate depending principally on (1) the available supply of the several 

 materials including water, (2) the intensity, duration and quality of the 

 light reaching the plant, (3) the amounts of the green leaf pigments, 

 (4) temperature and (5) the presence of certain enzymes. Any of these 

 factors of the plant's environment or composition may become limiting 

 in plant food synthesis, their degree of importance varying with condi- 

 tions. The immediate products of photosynthetic activity of the plant 

 are oxygen and carbohydrates. Oxygen for the most part is set free 

 and is in effect a by-product. Glucose is assumed to be the first synthetic 

 product of photosynthesis. Glucose may be considered a starting point 

 for the formation of more complex substances, such as the other hexoses, 

 disaccharides, polysaccharides, pentosans and pentoses. Starch is the 

 most common form in which carbohydrates are stored. They are also 

 stored frequently as sugars and sometimes they are transformed into 

 fats. The seasonal distribution of the more important of these materials 

 is discussed. Their storage is more common in or near the prgans where 

 they are later used. Carbohydrates are used principally for new tissue 

 building, for the retention of moisture, for increasing osmotic concentra- 

 tion and as a source of energy. Glucose particularly is a basic material 

 in the construction of plant tissues; for a great diversity of physiological 

 processes, pentosans are particularly important because of their water- 

 retaining capacity. Sugars are important in determining osmotic 

 concentration. Carbohydrates supply energy in the process of respira- 

 tion. The formation of certain pigments also depends on carbohydrates. 



