1909.] 



Vegetable Assimilation and Respiration. 



15 



erroi' were to be reckoned with. The leaves used were of several different types : Cherry 

 Laurel, thick and somewhat leathery ; Helianthus tuherosus, thin but coarse, and 

 Tropceolum majus, thin and delicate, both without a strongly supporting venation ; Lime 

 and Cercis, similarly contrasted as regards delicacy but with a very efficient supporting 

 network of veins. The templet, planimeter, and punch methods were all used in 

 determining areas. 



Attention has been concentrated on Helianthus tuherosus and the Cherry Laurel, since 

 they were also used for assimilation experiments. 



Tables showing Degree of Asymmetry existing in Various Leaves. 

 Explanatory Notes. 



The differences given were obtained by subtracting the dry weight of the right half- 

 leaf from that of the left, and the percentages have been calculated in terms of the 

 latter. The percentage differences are given in column 2, the actual differences in milli- 

 grammes per square decimetre in column 1. 



In each table, either the range of areas used in the series of experiments is given at the 

 head of the table, or the actual area cut from each half-leaf is given, in a special column, 

 for each experiment. Where the rotating punch* was used, the number of discs is given 

 instead of the area. The area of each disc was 0"804 square centimetre. 



In some cases the number of discs cut from each side was not the same : this was due 

 to the slightly unequal area of the two sides, or to different arrangement of the veins, 

 which were avoided where possible. For instance, in using the disc method with leaves 

 of Helianthus tuherosus, care was taken to make the discs equally representative of the 

 mesophyll on either side, whereas " symmetrical " cutting relative to the midrib would 

 have been impossible. This applies also to some of the experiments with Cherry Laurel. 

 The lateral veins in the larger leaves were sufficiently distant from one another to allow 

 of discs being cut from between them : absence of perfectly symmetrical placing of the 

 veins led to the cutting of different numbers of discs in such cases. Later, the supply of 

 large leaves was exhausted, and the smaller leaves had less prominent veins, so that there 

 was less objection to including them. Discs were then cut in equal numbers and from 

 symmetrical positions from the two sides. 



Table VII. — Cherry Laurel. Cut by rotating punch. 

 Number of discs from each half-leaf varied with size of leaf from 10 to 25. 





(1) 



(2) 





milligrammes. 



per cent. 





-12 



-1 -3 



2 



-25 



-2-8 



3 



-16 



-2-0 



4 



+ 27 



+ 2-5 



5 



+ 1 



Nil 



6 



-25 



-3-0 



7 



- 8 



-1 1 



8 



+ 2Q 



+ 3-3 



Averages of 1 — 8 



±17 



±2-0 



Leaves 1 — 8 taken together 



- 4 



-0-5 



Several leaves taken together — • 







8 leaves — Experiment 9 



-1-9 



-0-2 



6 „ „ 10 



-33 



-2-7 



7 „ „ 11 



+ 17 



+ 1-5 



6 „ „ 12 



+ 17 



+ 1-4 



* See p. 42. 



