589 
Balls. — Temfierahire and Growth. 
the slight irregularities in the stopping-point, noticed under conditions 
which are as uniform as I have been able to devise, may not be enough to 
prevent accurate determinations ; some other organism might be employed 
if this were found to be the case. 
The Time Factor in other Life-processes. 
This proof of the concrete and chemical nature of the time factor 
in growth leads one to hope that the same may be found to apply to the 
time factor in assimilation and respiration. From this point of view a fact 
recorded by Blackman might be suitable for further investigation ; namely, 
the low assimilatory maximum shown by Cherry Laurel leaves in their 
second year, as compared with the result which they give in their first 
year. If this depression of the maximum were due to the accumulation 
of a specific inhibitory body in the leaf cells, it should be possible to extract 
this body from two-year-olds, and supply it to the young leaves ; when 
it entered the cells of the latter their assimilatory maximum should at once 
fall. 
If, on the other hand, such treatment produced no effect, there would 
still be the possibility that this body really existed, but that the young 
leaves had the power of decomposing it, and that this power was lost 
in age. 
General Conclusions. 
1. The growth rate at various temperatures accords with the expecta- 
tions of Van ’t Hoff’s law. 
3 . The decrease, and ultimate cessation of growth at high temperatures, 
is due to the accumulation of katabolic products in the cells. 
3. This cessation is distinct from the disorganization of the protoplasm 
by heat, which results on a further rise of temperature to the death-point. 
4. The same products are formed at low, as at high temperatures, but 
with greater rapidity in the latter case. 
5. To the rapid formation of these bodies is due the injurious effect 
of prolonged exposure to sub-maximal temperatures, commonly known 
as the time factor. This time factor is identical with the phenomenon 
of ‘ staleness ’ in rich cultures of fungi. 
6. In the case of isolated cells these bodies diffuse out into the 
surrounding liquid. In multicellular organisms they have to be otherwise 
disposed of, probably by decomposition ; since the conditions under which 
this decomposition takes place must be fairly uniform in the interior of a 
higher plant, these latter show in consequence a well-marked ‘ Optimum ’, 
which is the expression of the internal struggle between the increasing 
rapidity of chemical change with rise of temperature, and the inhibiting 
effects of the accumulating katabolic products. 
