TISSUES AND SIMPLE ORGANS. 



109 



from a satisfactory explanation. Among others the author 1 has. 

 carried on some special investigations in regard to this problem. I 

 wish to state in advance that Schwendener for a time withheld 

 judgment in regard to my conclusions, 

 but that he defended some of my pro- 

 positions against attacks. Therefore 

 before entering more particularly into 

 Schwendener 's important investigations 

 I will here introduce my explanation. 



According to my interpretation, there 

 are two forces employed in the ascent of 

 the cell-sap: 1 , endosmosis ; 2, capillarity 

 the former a moving force, the latter 

 a holding or retaining force. Two forms 

 of elements represent the path in which 

 cell-sap moves; namely, living cells, the 

 wood-parenchyma and the medullary 

 rays in particular; also the dead ele- 

 ments, vessels and tracheids. Endos- 

 mosis acts as a propelling force in a 

 twofold way : by forcing water into the 

 dead elements at one point, while at 

 some more elevated point the living cells 

 take up the same and conduct it for a 

 short distance from cell to cell by endos- 

 motic suction. This proceeds in a longi- 

 tudinal direction to a point bearing less 

 water, hence upward, where it will 

 again be forced into the tracheal system. 

 Capillarity simply acts as a retaining 

 force, since the columns of water are self- 

 supporting. 2 In the remaining explana- 

 tions I will utilize the accompanying 

 diagramatic figure, in which A, B, C, 

 and D represent different elevations in FIG. 61. 



the stem, G a vessel, m the medullary rays, kp the woody paren- 



1 Berichte der Deutschen Botaniscbeu Gesellscbaft, 1883, and Sitz.-Ber. der 

 Berl. Akad., 1884. 



2 Zimmermann's investigations in d. Ber. der Deutsch. Bot. Ges., 1883. 



