88 DIFFUSION AND OSMOTIC PRESSURE 



more or less marked collapse. Also, the existence of differ- 

 ences in the turgor, and hence in the tissue tensions, of dif- 

 ferent parts of the body in higher plants, increases the 

 mechanical strength of the whole structure to a very marked 

 degree. The difference in tension between the pith and cor- 

 tex of many herbaceous stems is an illustration of this fact. 



c) Growth. Exactly what the relation between growth 

 and turgor may be cannot yet be stated, but there is good 

 evidence to show that in the presence of turgidity growth is 

 accelerated and in its absence retarded. Increase in thick- 

 ness of the cell wall cannot take place unless the protoplast 

 is kept turgid, and thus closely applied to it, as was shown 

 by Keinhardt. 1 Other evidence along this line is that 

 obtained by Klebs, 2 when he succeeded in causing a new 

 cellulose wall to form within the old one by keeping the pro- 

 toplast in a state of plasmolysis. Also the work of Bower 3 

 needs to be considered here. This author brings out very 

 clearly the fact that there is a close connection between wall 

 and protoplasm, by a study of the strands and fibers which 

 remain joining the protoplast to the wall in a plasmolyzed 

 cell. He thinks that the attachment of the protoplasm, which 

 results in the formation of these strands, is closely con- 

 nected with the process of wall-formation. The strands are 

 not usually opposite on the two sides of a common wall, and 

 thus apparently have no relation to pores through the wall. 



Experiments on the effect of light and temperature led 

 Copeland 4 to the conclusion that growth regulates turgor 

 rather than turgor growth. 



1 M. O. REINHARDT, " Plasmolytische Studien zur Kenntniss des Wachsthums 

 der Zellmembran," Festschrift fur Schwendener (1899), p. 425. 



2 G. KLEBS, " Beitrage zur Physiologie der Pflanzenzelle," Unters. aus d. bot. 

 Inst. zu Tubingen, Vol. II (1888), pp. 489-568. 



3 F. O. BOWER, " On Plasmolysis and its Bearing upon the Relations between 

 Cell-wall and Protoplasm," Quart. Jour. Microsc. Sci., Vol. XXIII (1885), pp. 157-67. 



*E. B. COPELAND, Ueber d. Einfluss von Licht u. Temperatur auf den Turgor, 

 Halle a. 8., 1896. 



