TRANSLOCATION OF ORGANIC FOOD-SUBSTANCES 579 



Sa/t'x if a bridge of phloem is left connecting k and k' (Fig. 67), and the fact 

 that the roots in K are formed mainly beneath this bridge shows that the nutrient 

 materials are transferred rapidly through the phloem longitudinally, but diffuse 

 horizontally only slowly. When a spiral strip of phloem is removed from a plant 

 in which the sieve-tubes do not anastomose or when two partial ringings are made 

 on opposite sides of the stem at a little distance from one another, according to 

 the structure of the plant, a more or less markedly decreased production of roots 

 is observed on the lower piece of stem, as was first shown by Hales, Cotta 

 and Knight. 



The phloem is hence the best conducting tissue for food-materials, but it is 

 not, as Sachs supposed (Flora, 1863, p. 23), specifically adapted for the special 

 transference of proteid, for non-nitrogenous materials also travel most actively in 

 the phloem, and are, according to Czapek, transferred too slowly through the 

 cortex or bundle-sheaths to satisfy the needs of tissues at any distance. When an 

 abundance of stored carbohydrates is present, the diminished growth after ringing 

 must naturally be due to the lessened supply of proteids, and it is probably seldom 

 the case that the conducting powers of the phloem are normally exercised to their 

 full limits. 



No downwardly directed transference of plastic substances normally occurs in 

 the wood, but an upward conduction with the water-current is always possible. 

 Thus Th. Hartig 1 observed the total depletion of starch from the roots of trees 

 (oak, &c.) although a broad ring of bark had been removed from the base of the 

 tree, and showed that buds beneath which the continuity of the phloem had been 

 broken still continued to develop. The experiments were not always successful, 

 probably owing to operative injuries or differences in constitution. Hanstein 

 obtained negative results with herbaceous plants, whereas Strasburger (1. c., p. 900) 

 observed that in some Umbelliferae fruit-formation continued after the continuity of 

 the phloem had been broken. Inflorescences and buds are, however, only capable 

 of a slight amount of development by means of their own reserve-materials, and 

 hence not only non-nitrogenous but also nitrogenous food-materials must have 

 been conveyed upwards along with the transpiration-current. This is also indi- 

 cated by certain experiments by Th. Hartig and other authors, and as a matter 

 of fact the exuded sap of many plants contains a certain amount of proteids, 

 amides, &c. The power of utilizing the transpiration-current for this purpose 

 probably varies under different circumstances and according to the plant examined, 

 and hence it is not surprising that A. Fischer was unable to detect any such 

 utilization of the water-current in translocation in any of the herbaceous plants he 

 examined. In woody plants usually only small amounts are conveyed in this 

 manner from the roots and the main stem, whereas the amount transferred becomes 

 very large when an increased consumption is caused by the renewed bud-formation 



1 Bot. Zeitung, 1858, p. 338 ; Sachs, Flora, 1863, P- 66 ; R. Hartig, Bot. Zeitung, 1888, p. 837 ; 

 Holz d. Rothbuche, 1888, p. 38; Anat. u. Physiol., 1891, p. 235; F. Miiller, Bot. Centralbl., 1889, 

 Bd. xxxix, p. 31 ; A. Fischer, Jahrb. f. wiss. Bot., 1891, Bd. xxil, p. 133 ; Strasburger, Leitungs- 

 bahnen, 1891, pp. 879, 915 ; Mer, Bot. Centralbl., 1892, Bd. LII, p. 188. 



P p 2 



