MOVEMENT OF MATERIALS IN THE PLANT 143 



was collected. It is apparent from these analyses that the sap contains less in- 

 organic substances and more organic materials in the earlier part of the season 

 than at the later dates. This is explained by the facts that organic materials 

 accumulate in the woody tissue of perennial plants during the summer, and that 

 they are rapidly removed to the growing regions with the opening of the follow- 

 ing spring; it is at the expense of this accumulated food that spring leaves are 

 formed. After the leaves develop, the sap contains inorganic substances 

 mainly, and spring bleeding thus becomes transformed into summer bleeding. 



The term bleeding thus denotes the exudation of sap from the woody tissues 

 of wounded plants, brought about by the absorption of water and dissolved 

 mineral substances by the parenchymatous cells of the root, and the movement 

 of this solution into the vessels of the xylem, in which it is carried upward to 

 the wound. The causes upon which this phenomenon is dependent have not yet 

 been found out. 5 



(c) Movement of water in the stem 1 depends upon a number of condition-. 

 Water moves upward in the xylem, as was shown in Malpighi's girdling experi- 

 ment. Sach's theory, which supposed that it traverses the vessel walls, was 

 proved untenable and is no longer upheld. The ascending current moves in 

 the lumina of the vesssels and tracheides, as is shown by the fact that wilting 

 promptly occurs when these are plugged. The following experiment demon- 

 strates this. A mixture of 20 parts of gelatine in 100 parts of water, melting at 

 33 and still liquid at г8°С. (at which temperatures plant tissues is not at all in- 

 jured) is prepared, and enough India ink is added to make the preparation 

 readily visible in the vessels. The stem of a leafy shoot is cut under this prepa- 

 ration, the latter having been warmed to зз°С. The liquid rises in the vessels 

 and is allowed to harden by cooling. A small piece is then cut from the base 

 of the stem, to give a fresh absorbing surface, and the cut end is placed in water. 

 After several hours wilting occurs in the leaves, while the leaves of a similar 



1 Votchal, Ueber die Bewegung des Wassers in den Pflanzen. Moscow, 1897 (Russian).* Böhm, 

 Joseph, Ueber die Ursache des Saftsteigens in den Pflanzen. Sitzungsber. (math.-naturw. Kl.) K. Akad. 

 Wiss. Wien. 48*: 10-24. 1863. Hartig, R., Die Gasdrucktheorie und die Sachs'sche Imbibitions-Theorie. 

 Berlin, 1883. Strasburger, Eduard, Ueber den Bau und die Verrichtungen der Leitungsbahnen in den 

 Pflanzen. (Histologische Beiträge, Heft 3.) Jena, 1891. Askenasy, E., Ueber das Saftsteigen. Verhandl. 

 Naturhist.-Med. Ver. Heidelberg, n. F. 5: 325-345- [Gesammtsitzung vom 7. Dez., 1894, und 1. Febr., 

 1895- Heft 4, dated 1896.] Idem, Beiträge zur Erklärung des Saftsteigens. Ibid, 5: 429-448. [Ge- 

 sammtsitzung vom 6. März, 1896. Heft 4. Vol. dated Heidelberg, 1897 ] Godlewski, E., Zur Theorie 

 der Wasserbewegung in den Pflanzen. Jahrb. wiss Bot. 15; s 69-630. 1884. [Schwendener, S., Unter- 

 suchungen über das Saftsteigen. Sitzungsber. (math.-naturw. Mitth.) K. Preuss. Akad. Wiss. Berlin 

 1886: 355-396. 1886. Idem, Vorlesungen über mechanischen Probleme der Botanik. Leipzig, 1909-] 



« Molisch showed that the phenomenon of sap exudation from holes and cuts in the upper 

 regions of palm stems is not due to a pressure normally present in the plant, but that the pres- 

 sure here indicated is brought about as a result of wounding. The cells near the cut surface 

 undergo an alteration, and bleeding begins only after enough time has elapsed to allow this 

 alteration to occur. The altered cells resemble gland cells and secrete the liquid. But it 

 appears improbable that all the cases of bleeding are to be thus explained. See: Molisch, 

 Hans, Botanische Beobachtungen auf Java. (III. Abhandlung.) Die Secretion des Palm- 

 weins und ihre Ursachen. Sitzungsber. (math.-naturw. Kl.) K. Akad. Wiss. Wien 107': 1247- 

 1271. 1898. Idem, Ueber localen Blutungsdruck und seine Ursachen. Bot. Zeitg. 60: 

 45-63- 1902. 



