( 227 ) 
lower temperature in the seeds with a higher protein content is 
perhaps connected with the fact that the optimum for proteolytic 
generally lies lower than for diastatic ones. 
In conclusion I mention a few experiments with capitula of Crepis 
biennis. I only made observations from 30°—50°; at each of the 
temperatures employed a falling-off was observable, which was very 
marked and gave an almost straight line. The experiments are too 
few in number to allow of a definite conclusion being drawn but 
the marked decline is in this case also most probably influenced by 
a want of respiratory material. According to the observations the 
respiration increases during the first hour right up to 45°, while the 
temperature limit of life is only a very little higher; after a 6 hours’ 
exposure to 45° the flowers were dead. 
My results are therefore as follows: 
1. the theory of Blackman is also applicable to respiration to the 
extent that: o 
a. the rule of van’t Hoff- Arrhenius holds good from 0° to 20 —25 . 
b. the optimum may be displaced with the tiine of observation. 
c. the falling off at 40°, 45°, and 50° has a logarithmic course in 
seedlings. 
2. the course of respiration depends very much on the nature of 
the reserve food. 
Utrecht , Botanical Laboratory. 
Chemistry. — “On retrogressive melting-point lines . By Prof. 
A. Smits. (Communicated by Prof. J. D. van der Waals). 
(First Communication.) 
Applying the method indicated by van der Waals 1 ) we find for 
the melting-point line under the vapour pressure the following 
equation: 
dx^_ 1 /dx L \ (*L — «g) K V 9— 4 -Qsl) -(Vl- Vs)QlG 
dt T JT (Vg— V L ){xl—9 9 ) v S— ” g )V L + Vg\ 
in which Q sl = mol. heat of melting of a compound of the con¬ 
centration as ; 
Q m = differential mol. heat of mixing of the melted com¬ 
pound with a solution of the concentration xl; 
Q lg — mol. heat of evaporation of a solution of the con¬ 
centration xl • 
l ) Versl. Kon. Akad. v. Wet. 28 Febr. 1885 and Rec. Trav. chim. 5, 336 (1886). 
