Physiological Studies in Plant Anatomy 133 
the earlier observation of Schnee that the protoplasm within the 
suberin lamella will plasmolyse, although slowly. He therefore con¬ 
cludes that the protoplast within the suberin lamella remains alive 
for many years in perennial tissues and its surrounding suberin 
lamella must therefore remain permeable to water and the dissolved 
substances necessary to support life. 
Osterhout(i 9 ) has shown that plasmolysis is a good criterion of 
the vitality of a protoplast but he has also shown that there are many 
states of contracted protoplasm which must be distinguished from 
true plasmolysis. We do not feel competent to challenge Mylius’s 
observations upon plasmolysis from our more limited series of 
observations but would emphasise the fact that the endodermal 
protoplast will contract away from the wall under a most varied series 
of reagents, ranging from plasmolysing agents to strong acids. In all 
such cases it appears as a band stretching across the cell and is 
invariably attached to the Casparian strip. We have no confidence 
that in any case could this appearance be ascribed to a true process 
of plasmolysis, neither is it any evidence of the penetration of the 
suberin lamella by any of these reagents when acting upon an 
endodermis in an uncut plant. 
On the other hand, there is convincing evidence that the cells of 
the secondary endodermis are completely impermeable to toxic 
electrolytes in strong concentrations which readily penetrate proto¬ 
plasmic membranes if they can achieve contact with them. This 
evidence is a strong argument in favour of the conclusion that the 
suberin lamella is impermeable to all inorganic solutes. Mylius quotes 
the experiments of Schwendener on the penetrability of secondary 
and tertiary stages of the endodermis, which are really tests of the 
permeability of the suberin lamella. These experiments are not free 
from objection owing to the reagents employed. Thus in the experi¬ 
ments in which he looked for inward diffusion through the endodermis 
of iodine from various aqueous solutions, it must be remembered 
that the suberin lamella is impregnated with fatty substances which 
dissolve iodine, so that its slow penetration is probably due to its 
solubility in the lamella. The use of tannin is not open to this objec¬ 
tion and after tannin had been sucked through the rhizome of Iris 
germanica for a day sections of the rhizome placed in iron salts 
showed no trace of tannin in the cells of the endodermal cylinder or 
cortex. In similar experiments with the roots of Iris germanica 
Schwendener found that the tannin passed out through the endo¬ 
dermis by the passage cells only. Tannin is such an active precipitant 
that although the above experiments are very convincing, it might 
