208 
Walter Stiles 
Miss Delf (1916) in onion leaves. How general such a complication 
may be there is no evidence to tell; it is a possibility which should 
not be lost sight of in dealing with problems connected with the 
relations of the cell to solutions. 
Where such a complication is present the course of plasmolytic 
shrinkage will obviously differ from the normal case where the cell 
wall is as completely permeable to the solute as to water. The rate 
of separation of the protoplast from the cell wall will take place more 
slowly, as it will take time for the solution outside the protoplast to 
reach the plasmolysing concentration. 
The Effect of Tissue Tensions on the Water 
Relations of Cells enclosed in Tissues 
That different cells in the same organ maybe subjected to different 
external pressures from surrounding cells and tissues is indicated by 
the changes in shape which pieces of tissue may undergo when iso¬ 
lated from the intact plant body. Thus the curvatures of longitudinal 
strips of dandelion scapes mentioned in an earlier section of this 
chapter indicate that in the intact scape the central tissue must have 
been in a state of compression, for it elongates on isolation of the 
strip, while the epidermal tissue contracts, showing that this tissue 
was stretched and under tension. Investigations on tissue strains 
have been numerous, but a discussion of this subject does not lie 
within the scope of this work. For general information on the sub¬ 
ject the reader is referred to Chapter V of the second volume of the 
English edition of Pfeffer’s Physiology of Plants (1903). But the 
presence of these strains must influence very materially the water 
relations of the cells in tissues where such strains exist. Yet as far 
as I know this question is only discussed in one place, namely, in 
the excellent paper by Hofler (1920) on the osmotic relations of 
the plant cell. Hofler says himself that the subject has never been 
investigated either theoretically or experimentally. The relations are 
obviously complex. Let us consider a tissue which has been immersed 
in a hypertonic solution, or which has lost water by evaporation, so 
that all the cells within it are turgorless. If such a tissue is now 
immersed in water, the latter enters at first on all sides so that 
neighbouring cells as they swell press against one another. The only 
space then into which the cells can stretch further is the intercellular 
space system. Hence the cells become deformed with a non-uniform 
stretching of the cell wall, and consequently an uneven distribution 
of the wall pressure. A state of equilibrium is still possible under 
