3 6 
F. F. Blackman. 
The laboratory methods that have been most used to bring 
about the condition of reduced vitality with accompanying cessation 
of more or fewer of the higher cell-functions are drought, heat, 
mechanical disintegration and drugs. 
The complete dessication of a vegetative cell of a higher plant 
generally produces complete death, a cessation of all the vital 
functions with no possibility of recovery on wetting again. With 
the lower plants (many Algae and some Mosses and Liverworts) 
complete recovery of all functions may take place quickly on 
wetting after prolonged dessication and such also is the case with 
the specialised propagative parts of higher plants (spores and seeds). 
Between these two extremes there are undoubtedly intermediate 
cases in which there is a recovery of the lower cell-functions and 
not of the higher, cases for example in which there is recovery of 
the functions of respiration and turgidity without recovery of the 
assimilatory function. Considering the matter from an evolutionary 
standpoint it would appear to be normal for a cell to be uninjured 
by drying up. When the effect is death we may attribute this to 
some secondary cause. 
As regards the effect of heat we must carefully distinguish 
between the effect of heating cells with high and with low water 
content. Air-dry seeds (with their 10 % of water) will stand a much 
higher temperature than the same seeds when once wetted. Seeds 
when completely freed from every trace of water will survive 
heating to such high temperatures as 120 n C as Just showed in 1877. 
The explanation of this lies in the fact that dry proteids are not 
coagulated by heating to 100°C ; and Farmer has shown that the less 
the percentage of water contained in solid egg-albumen the higher 
it must be heated to render it subsequently insoluble. 
This resistance to heat when dried probably holds for some 
of the vegetative cells which can withstand dessication: one 
may not therefore assume in a case in which, for example, a dried 
leaf after being heated, still retains the power of liberating oxygen 
in the light when wetted, that this phenomenon is due to nothing 
more complex than an enzyme. It may possibly be due to residual 
protoplasmic activity of a higher order. The bearing of these 
considerations on recent controversy will be apparent presently. 
Mechanical disintegration was first successfully used by 
Buchner in his work on yeast. The effect varies with the com¬ 
pleteness of the procedure and the nature of the plant-material. 
The writer has found that if wheat be ground up finely and then 
