152 PHYSIOLOGY OF NUTRITION 



tissues. By comparing the distribution of these substances as shown in the 

 seed with that exhibited in the seedling and in different regions of the older plant, 

 Sachs reached his conclusions as to the paths of translocation. He found, for 

 example, that the cortex contains cells that are filled with starch grains during 

 germination, and that these cells form a continuous series (which he called the 

 starch sheath) reaching outward from the cotyledons into all parts of the 

 plantlet. From these observations he concluded that it is in this sheath that 

 starch moves from the cotyledons into other regions, as growth proceeds. The 

 sort of observations on which this conclusion was based bear, however, only 

 upon the distribution and accumulation of the substances in question, in the 

 various organs of the plant; the fact that a continuous series of cells all contain 

 a certain substance does not indicate that the substance in question is moving 

 through those cells. In the case of the starch-filled cells above mentioned, the 

 subsequent experiments of Heine 1 showed that this material is not there in 

 process of translocation, but that the contents of these cells represent merely 

 local accumulations. This author removed rings of tissue from stems of young 

 seedlings, so as to remove the starch sheath at the region of girdling, and found 

 that such treatment neither hindered the development of the plants nor lessened 

 the amount of starch in those regions of the sheath beyond the wound. There- 

 fore, in this case also, the organic materials must have moved through the phloem 

 (leptome) of the bundles, which was not injured by the girdling operation. 

 Some of the plastic material passing through the uninjured phloem found its 

 way to the sheath cells and there accumulated locally as starch. 



There are also available some studies, by Sachs, Sapozhnikov, 2 and others, 

 bearing upon the translocation of organic substances from the leaves, where they 

 are formed, to other portions of the plant. As carbohydrates are produced in 

 the leaves they continually move into the stem. Comparison of the loss of 

 carbohydrates from attached leaves with the loss, in the same time, from similar 

 leaves that have been detached from the plant, shows that this rate of loss is 

 more than five times as great in the first case as it is in the second. This obser- 

 vation indicates clearly that translocation of carbohydrates from leaves to stem 

 actually occurs. Carbohydrates disappear from the detached leaves only 

 through local consumption, and the rate of its disappearance is much lower 

 than in the case of leaves that remain attached to the plant. This movement 

 of carbohydrates takes place through the phloem. 3 There is a daily periodicity 

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

 ment occurs, according to Sapozhnikov, during the early hours of the night, 

 between 7 130 and 1 1 130. 



In perennial plants the accumulated material formed during the summer 

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



1 Heine, H, Die physiologische Bedeutung der sogenannten Starkescheide. Landw. Versuchsst. 35 : 

 161-193. 1888. 



2 Sapozhnikov, Die Bildung der Kohlehydrate in den Blattern and ihre Bewegung in der Pflanze. Moscow, 

 1890. (Russian.)* Idem, 1890. [See note 2, p. 32.] Idem, 1891. [See note 2, p. 39.] Idem, 1893. [See 

 note 2, p. 32.] 



3 Czapek, Friedrich, Ueber die Leitungswege der organischen Baustoffe im Pflanzenkorper. Sitzungsber. 

 (math, naturw. Kl.) K. Akad. Wiss. Wien 106: 11 7-1 70. 1897. 



