634 



SCIENCE 



[N. S. Vol. XXVIII. No. 723 



worked out by Miss Matthsei,^ the rate of 

 assimilation by cherry-laurel leaves being 

 measured from — 6° C. to + 42° C. Up 

 to 37° C. the curve rose at first gently and 

 then more and more steeply, but on cal- 

 culating out the values it is found that the 

 acceleration for successive rises of 10° C. 

 becomes less and less. Between 9° C. and 

 19° C. the increase is 2.1 times, the highest 

 coefScient measured, and exactly the same 

 coefficient as for respiration in this plant, 

 which in itself is a striking point, seeing 

 how different the processes are. The de- 

 crease of the coefficient with successive 

 rises is a state of things which is quite 

 general among non-vital reactions. A 

 critical consideration of the matter leads 

 one to the conclusion, however, that this 

 failure to keep up the temperature ac- 

 celeration is really dtie to secondary causes, 

 as is also the appearance of an optimum at 

 about 38° C. Some of these causes have 

 been discussed by me elsewhere,' and I 

 hope to bring a new aspect of the matter 

 before the section in a separate communi- 

 cation. The conclusion formerly come to 

 was that probably in its initial stages as- 

 similation at these very high temperatures 

 started at the full value indicated by a 

 theoretically constant coefficient, but that 

 the protoplasm was unable to keep up the 

 velocity, and the rate declined. It must 

 be borne in mind here that quite probably 

 no chloroplast since the first appearance 

 of green cells upon the earth had ever 

 been called upon for anything like such a 

 gastronomic effort as these cherry-laurel 

 leaves in question. It is not to be won- 

 dered that their capacities speedily de- 

 'clined at such a banquet, and that the 

 •velocity-reaction of anabolic synthesis 

 traces a falling curve in spite of the keep- 



'Phil. Trails. Roy. Soc, Ser. B, Vol. CXCVII., 

 1904. 



° " Optima and Limiting Factors," Annals of 

 Botany, Vol. XIX., April, 1905. 



ing up of all the factors concerned, to wit, 

 temperature, illumination and supply of 

 CO,. This decline is not permanent, but 

 after a period of darkening the power of 

 assimilation returns. Physical-chemical 

 parallels can easily be found among cases 

 where the accumulation of the products of 

 a reaction delays the apparent velocity of 

 the reaction, but this complicated case may 

 be left for further research. 



In relation to assimilation, then, we 

 must say that owing to secondary causes 

 the ease is not so clear over the whole 

 range of temperature as that of respira- 

 tion, but that at medium temperatures we 

 have exactly the same relation between 

 reaction-velocity and temperature. 



"We may consider now some data upon 

 the combined net result of anabolic and 

 katabolic processes. Such total effects are 

 seen in their clearest form among uni- 

 cellular saprophytic organisms for which 

 we have a few data. Mile. Maltaux and 

 Professor Massart^" have published a very 

 interesting study of the rate of division 

 of the colorless flagellate ChilomO')ias para- 

 mcecium and of the agents which they 

 say stimulate its cell-division, in par- 

 ticular alcohol and heat. 



They observed under the microscope the 

 time that the actual process of division 

 into two took at different temperatures. 

 Prom 29 minutes at 15° C. the time 

 diminished to 12 minutes at 25° C, and 

 further to 5 minutes at 35° C. The veloci- 

 ties of the procedure at the three tempera- 

 tures 10° C. apart will therefore be in the 

 ratio of 1 : 2.4 : 5.76, which gives a factor 

 of 2.4 for each rise of 10° C. 



Now we are told by the investigators 

 that at 35° C. Chilomonas is on the point 

 of succumbing to the heat, so that the 

 division rate increases right up to the death 

 point, with no sign of an optimum effect. 



'° Maltairs: and Massart, Recueil de I'Institut 

 iotanique Bruxelles, Tome VI., 1906. 



