ASSIMILATION AND TEMPERATURE. 



31' 



minimum temperature for assimilation by Anacharis, Lepidium, 

 and Betula as 3-5 C. ; and Heinrich 1 gives it as 2. 5-4. 5 C. 

 for Hottonia. 



The maximum temperature at which assimilation can occur 

 in Anacharis ~ is between 45 and 50 C. ; in Hottonia, 3 just be- 

 low 56 C. 



The optimum* temperature for Hottonia appears to be not 

 far from 31 C. 



showed no trace of starch. The plants were then distributed in three rooms 

 of the temperatures mentioned in the annexed table, and with the results there 

 detailed : 



After 



2 hours. 



3 hours. 

 5 hours. 



13 hours. 



12.8-13.7 C. 



The first starch granules appear 



in the chlorophyll cells on the 



margin of the leaves. 

 Starch in the whole tip, margins, 



and petiole. 

 Starch in the whole upper half of 



the leaf. 

 The whole leaf contained starch. 



5.9-6.5 C. 



No starch. 



Some traces of starch at 

 margins of the leaves. 



Tip and narrow edge with 

 starch. 



Margin with much, sur- 

 face with little starch. 



0.3-0.5 C. 



No starch 



1 Versuchs-Stationen, xiii., 1871, p. 136. 



2 Schutzenberger and Quinquaud : Comptes Eendus, Ixxvii., 1873, p. 272. 



3 Heinrich: Versuchs-Stationen, xiii., 1871, p. 136. 



4 Heinrich's figures are so instructive that they are here presented in the 

 following table, which gives the number of bubbles of gas passing off from the 

 cut surface of single leaves of Hottonia during the space of five minutes : 



Temp. C. No. of bubbles. 



11 145-160 



12 180-190 



13 215- 



15 245-255 



!" .. 255-265 



21 325-360 



22 375- 



25 390-450 



31 547-580 



37 420-517 



43 225-255 



50 110-220 



56 



The student must be reminded that the amount of gas which comes off 

 in this experiment with submerged plants is not an exact measure of the 

 assimilation. 



