Brown.—Studies in the Physiology of Parasitism. I. 333 
Senecio ( Kleinia) articulata\ Transverse sections of stem, the sides being cut 
away so that the sections take the form of narrow strips including the central tissue 
of the stem. 
Cotyledon rosacea : Transverse sections of leaf, prepared in the same way as the 
immediately preceding. 
In all cases the tissue discs or strips were prepared according to 
the method for quantitative experiment; previous to use they were injected 
with water. 
The following account of an experiment with transverse axial strips of 
pith of Senecio articulata will serve to illustrate the sequence of phenomena 
observed: 
Strips placed in standard extract at 4.5 p.m. 4.20, strips coherent; 
ditto at 4.25 and 4.30. 4.35, coherence gone. 
A strip at this stage is placed for three minutes in a 5 per cent, 
solution of KN 0 3 in which a little eosin is dissolved ; then washed in 
5 per cent, solution of KNO s . On microscopic examination, this strip 
shows as many fully plasmolysed cells in the central region as a strip which 
has not been exposed to the action of the extract. The cells of the strip 
exposed to the extract only differ in appearance from those of the latter 
inasmuch as the cell-walls do not appear so well defined and are more 
transparent. There is no marked swelling of the walls. 
If a strip which has been treated with extract be pulled apart at 
this stage, it shows a characteristic appearance along the line of separation. 
Separation follows the line of the cell-walls, the cells on either side being 
left intact. When, on the other hand, a strip of tissue which has not been 
treated with extract is pulled apart at the centre, the line of separation 
passes as often as not across the cells so that the tissue at the margin 
possesses a ragged appearance. This phenomenon is taken as indicative of 
the action of the extract upon the middle lamella, and it shows that 
the latter is in an advanced state of solution at a time when the cells 
are still alive and when the remaining portions of the cell-wall still possess 
their mechanical properties. 
4.50— a strip on plasmolysis still shows a large proportion of live cells 
in the central region, quite close up to the line where the strip separates on 
being pulled. The tissue is now very difficult to handle without producing 
damage. Thus when a cover-glass is laid on a portion of the central tissue, 
the latter becomes a disorganized mush. The collapsed cell-walls of this 
mush show a flaky or layered appearance, indicating solution of certain cell- 
wall constituents, a process which results in the cell-wall losing its mechanical 
properties. 
5.5 and 5.20—a fair proportion of central cells still plasmolysable. 
5.50— central region now shows only occasional living cells, the proto¬ 
plasts of which are reduced by plasmolysis to very small globules ; the 
