580 TRA NSL OCA TION 



and development induced by the removal of the leaves. Similarly after flowering 

 commences large quantities of reserve-materials are conveyed to the ripening 

 fruits. 



The upward conduction probably takes place to a large extent in the phloem 

 also, and the conclusion arrived at by certain authors l that the phloem of trees is 

 incapable of upward translocation is hardly supported by a careful consideration of 

 the available experimental evidence. Indeed the converse appears to be true, for 

 when a branch is planted upside down the assimilatory products are still conveyed 

 from the leaves to the root by the sieve-tubes, that is in the opposite direction to 

 the normal one. 



The diminution of growth must be proved to be due to a deficiency of nutri- 

 ment before it can be used as an indication that the continuity of the conducting 

 channels has been interrupted, for operative injuries may directly induce diminished 

 growth. Hence arose the incorrect supposition that the phloem is incapable of 

 upward translocation, from the fact that the stem of a tree ceases to grow in thick- 

 ness below the point ringed. As a matter of fact food-materials are conveyed in 

 this direction when growth is excited by an injury, or when buds commence to 

 develop and consume food-material, while in some cases reserve-materials are even 

 deposited in the non-growing portion of the stem. Growth in thickness also 

 ceases in the stems of Periploca and Tecoma below the injury, although after being 

 ringed the continuity of the phloem is maintained by their medullary phloem 

 strands 2 . Again, the most abundant supply of food is unable to induce growth where 

 no tendency to growth exists. Similarly when a flower is not fertilized, the peduncle 

 does not develop further, although otherwise as the fruit-stalk it would have func- 

 tioned as an extremely active translocatory channel 3 . Tittmann 4 has shown also 

 that according to circumstances the formation of callus tissue may be induced 

 either upon the upper or under cut surface of a twig. 



Sieve-tubes 6 . These are especially active translocatory channels and contain an 

 abundance of both nitrogenous and non-nitrogenous substances. Thus G. Kraus" 

 found in the sap escaping from the sieve-tubes of a cucumber 7 to 10 per cent, of 

 solid or disssolved substances, of which 20 per cent, were proteids, 30 per cent. 

 amides, and 38 per cent, soluble carbohydrates, while among the ash constituents 

 compounds of potassium and phosphoric acid were most abundant, and those of 

 magnesium next. This coincides with Schimper's micro-chemical studies (Flora, 

 1890, pp. 228, 260), according to which the phosphoric acid occurs mainly in the 



1 Cf. Th. Hartig, Bot. Zeitung, 1888, p. 339 ; Sachs, 1. c. ; Strasburger, 1. c., p. 891 ; A. Fischer, 

 I.e., p. 150. 



3 Jost, Bot. Zeitung, 1893, p. 120, and the literature here given. 



3 On similar actions of this kind, cf. de Vries, Jahrb. f. wiss. Bot., 1891, Bd. xxn, p. 50; 

 Busch, Ber. d. Bot. Ges., 1889, Generalvers., p. 29; Jost, Bot. Zeitung, 1891, p. 530; 1893, p. 131. 



4 Tittmann, Jahrb. f. wiss. Bot., 1895, B< 1. xxvn, p. 193. 



5 Literature: Haberlandt, Physiol. Anat., 1896, 2. Aufl., p. 286 ; Strasburger, Leitungsbahnen, 

 1891, pp. 476, 918; A. Fischer, Unters. ii. d. Seitenrohrensystem d. Cucurbitaceae, 1884; Sitzungsb. 

 d. Sachs. Ges. d. Wiss., 1885, p. 245; 1886, p. 291. 



6 G. Kraus, Siebrohreninhalt von Cumrbiia, Sitzungsb. d. Naturf.-Ges. z. Halle, Feb., 1894. 



