( 219 ) 
Botany. — “The influence of temperature on the respiration of the 
higher plants.” By J. Kuyper. (Communicated by Prof. F. Went.) 
In 1905 Miss Matthaei 1 ) carried out some investigations on assi¬ 
milation in the leaves of Primus Laurocerasus. The figures thus 
obtained led Blackman’) to some theoretical considerations entitled. 
“Optima and limiting factors.” * 
According to these views there arises in the curve representing 
the variation of a physiological process with temperature an optimum 
in consequence of a harmful influence at higher temperatures, which 
influence increases with the temperature. If the process were to follow 
the laws of a chemical reaction completely, then the rule ot van 
’tHoff-Arrhenius would hold good for any temperature interval ot 
10°; the figures show, however, that in the case of assimilation this 
rule only applies between 0’ and 20°-25°. If by this rule the 
theoretical values are calculated for higher temperatures they prove 
to be much higher than those found experimentally. At the same 
time these values decrease, in proportion as the objects have been 
exposed for a longer time to the higher temperature. According to 
Blackman the calculated value agrees with that found by exterpola- 
tion to zero time from the series of figures found by observation in 
successive equal time intervals at constant temperatures. 
As a corollary of this view it follows, that an optimum is not an 
absolute point but changes with the duration of the observations. 
The influence which the process undergoes after a length of time 
at a higher temperature acts’ as “limiting factor . These limiting 
factors are discussed in detail in Blackman s paper. 
I have investigated the extent to which this theory is applicable 
to the normal respiration of seedlings and in the following pages I 
propose to give a preliminary account of the results obtained. 
I P used as measure of respiration the liberation of CO„ which 
. was estimated according to Peefeer’s method ) The temperatu 
was kept constant within 0.2“ C.; in order , to determine the time 
required by the objects to attain the constant temperature the course 
of the temperature was followed tbermo-electrically in a few cases, 
it was not possible to do this continually in the botanical laboratory. 
The seedlings were placed, as free from each other as possible, 
on aluminium plates arranged round an axis in the respuation vesse , 
” i) G. L. G. Matthaei, Philosophical Transactions, voL '97 B, p. 47, 1905. 
8) F. F. Blackman, Annals of Botany, vol. XIX, p. 281, 1 wo. 
- - dem botan. Institut zu Tubingen, Bd. 1, 
