Residual Vitality. 35 
energy for the synthetic production of substances suitable for the 
food of man. 
Before considering the present state of experimental work on 
the functions exhibited in states of reduced vitality, a few words on 
the theoretical aspect of the subject may be desirable. 
The functions of a plant-cell are justifiably to be regarded as 
a series, passing from simpler to more complex, the possibility 
of carrying on the latter depending upon the efficiency of the 
former subordinate ones. In most,modes of death all these are 
not destroyed at once, and speaking quite broadly, they cease in order 
from above downwards. The phenomena of irritability are 
lost before the metabolic machinery fails and even the casual 
application of narcotic and other drugs will serve to throw the 
former out of action and leave the latter unimpaired. Growth too 
by the same two tests is found to be a function superposed on such 
metabolic processes as suffice for merely continued healthy 
existence. The organisation of the primordial utricle which enables 
it to act as a semi-permeable membrane and remain turgid, is lost 
(during slow death by starvation) at a point previous to the rapid 
collapse of the respiratory function 1 . Assimilation again may be 
entirely destroyed by the prolonged action of an injuriously high 
temperature before the respiration is at all prejudicially affected 2 . 
The enzymic functions of a cell often persist after respiration and 
all higher functions have ceased. 
In such a prolonged moriturient sequence no point can be fixed 
as an absolute death-point for the cell. The loss of the power of 
keeping turgid (which can be conveniently measured by the 
corresponding incapacity for being plasmolysed) furnishes an 
obvious conventional point, front beyond which there can pre¬ 
sumably be no return, at all events for the cells of the higher 
plants. 
1 The writer kept a cut-off Tropaeolum leaf for ten days in 
the dark without water but in an atmosphere saturated with 
moisture and estimations of the weight of the leaf and its 
CO, production were made at frequent intervals. For about 
nine days there was no serious loss of weight and then 
suddenly the organisation of the primordial utricles failed 
and the cell sap escaped into the intercellular spaces and 
out through the stomata, leading to a rapid loss of weight. 
Soon after this the respiration which previously was fairly 
high came down with a run towards zero. 
2 The writer has found that if a single leaf of Cherry Laurel 
be kept at a temperature of 35°C in the light and supplied 
with C 0 2 , after about 36 hours its assimilation suddenly 
begins to fail and diminishes to zero leaving the leaf in a 
condition in which its respiration is still normal and it 
produces as much C 0 2 in the light as it did before in the 
dark. 
