TISSUES AND SIMPLE ORGANS. 105 



quantity than in imbibition, hence an irregular quantity), but from 

 external causes, and always with the result that the structure of the 

 grain is permanently changed. Imbibed membranes, as well as 

 starch-grains after drying, can take up a definite amount of water 

 and assume their original volume ; swollen, similarly treated cell- 

 walls and starch-grains will not assume their original volume (CoR- 

 RENS). Imbibition is therefore something specific, a taking-up of 

 water without change in structure, a change which can not be 

 equally well designated by the term c 4 capillary action. ' ' 



The ready displacement of water in membranes, mentioned by 

 SACHS, 1 and the great frictional resistance which must exist accord- 

 ing to physical laws, are in direct opposition. Moreover, the above- 

 mentioned displacement has not been demonstrated by unimpeach- 

 able experiments. Imbibed membranes, for example of Lami- 

 naria, show this high frictional resistance according to the investi- 

 gations of SACHS. The hypothesis of Sachs had its origin at a time 

 when the anatomical-physiological conception, which later brought 

 about such excellent results, was but little understood. At that 

 time the best workers in our branch of science treated the cell-forms 

 of the plant-body according to a strictly anatomical method based 

 upon the evolutionary history of development so characteristic of 

 ^AGELI and his school. The conclusions of Nageli and Schwen- 

 dener's 2 critical speculative studies concerning this subject point 

 to wholly different results and do not formulate a concluded theory. 

 Although these studies preceded the advance made in our knowl- 

 edge concerning endosmosis, through the investigations of Pfeft'er 

 (1877) the conclusions of Nageli still hold good. They are as fol- 

 lows : "It only remains for us to distribute the water-moving 

 forces among certain numerous points. Since there is no reason 

 why we should concentrate them in definite cells of the tissues, it 

 seems most natural to locate them in each and every cell containing 

 cell-sap. Only when the energies of the tree are equally dis- 

 tributed in all cells are such diminished tensions, as occur in the 

 plant, explainable." SCHWENDENER'S 3 more recent investigations 

 verify his former conclusions as well as those of Nageli. Based 

 upon these two works (1877 and 1886), and also upon Pfeffer's 



1 Porositat des Holzes: Arbeiten des Bot. Inst. in Wurzburg II, 1879. 



2 Das Mikroskop, 1877. 



3 Sitz.-Ber. der Berliner Akademie, 1886. 



