150 PHYSIOLOGY OF NUTRITION 



of carbohydrates takes place through the phloem. 1 There is a daily periodicity 

 in the movement of carbohydrates out of the leaf ; the maximum rate of 

 movement occurs, according to Sapozhnikov, during the early hours of the 

 night, between 7:30 and 11:30. 



In perennial plants the accumulated material formed during the summer 

 in never wholly consumed in the same season; a large part is accumulated and 

 remains in the plant until the following spring. The renewed activity of early 

 spring and the development of new shoots and leaves occurs at the expense of 

 organic material accumulated in the preceding year. Accumulation begins 

 very early in the season in some plants — in May, for instance, in the case of the 

 maple; in other plants it begins later — in the oak, for example, in July, and in 

 the Scotch pine, in September. The material first accumulates in the young 

 twigs, from which it gradually moves down the stem until the roots also are 

 filled. Accumulation ceases at the end of the summer or in the autumn — 

 not until the middle of October in the case of the pine, for example. In winter 

 the accumulated material, consisting mainly of oil and starch, fills all the 

 pith, the medullary rays, the cortex and some parts of the xylem. 



The solution of the accumulated material begins in early spring. As it 

 dissolves it passes through the medullary rays into the vessels of the xylem, in 

 which it moves to the growing regions, as has been pointed out. If the young 

 twigs are killed by a late spring frost, after the winter reserve has been used up, 

 the death of the tree may follow. 



Organic materials are removed from storage tissues into other tissues only 

 when they are being consumed in the latter or are moving through these tissues 

 into still more distant regions. 2 If the embryo is removed from a seed of 

 maize or barley, for example, and if the remaining endosperm is planted in moist 

 soil, then the starch of the endosperm is neither removed nor converted into 

 sugar. If, however, the endosperm is placed on the point of a little cone of 

 plaster of Paris, the lower end of which dips into water, the starch is then dis- 

 solved and the resulting sugar diffuses into the water below. Maize endo- 

 sperm is thus completely emptied of starch in from thirteen to eighteen days and 

 a considerable quantity of carbohydrates appears in the water. Similar experi- 

 ments may be performed with bulbs, roots, rhizomes and branches. Lack of 

 oxygen in the atmosphere about the endosperm, or the presence of ether or 

 chloroform vapor, terminates this process. 



Summary 



1. Movement of Materials in General. — Substances enter the plant body at certain 

 parts of its periphery, and then move to distant regions, being in many cases decom- 

 posed and their elements being recombined in various ways during their stay in the 

 plant. Some materials remain in the plant until its death, while others are continuously 

 or intermittently given off to the surroundings. 



i Czapek, Friedrich, Ueber die Leitungswege der organischen Baustoffe im Pflanzenkörper. Sitzungsber. 

 (math, naturw. Kl.) K.Akad.Wiss. Wien 106: 1 17-170. 1897. 



- Puriewitsch, K., Physiologsche Untersuchungen über die Entleerung der Reservestoffbehälter. 

 Tahrb. wiss. Bot. 31 : 1-76. 1898. 



