1910.] 



Vegetable Assimilation and Respiration. 



425 



This method was not complete in all its details when my earlier paper was 

 written, and must now be described more fully than was possible at that 

 time. 



(1) The Stamping Method. 



In this method equal areas are marked out at the beginning of the experiment on 

 both the control and the experimental half-leaves, by means of an inked rubber stamp. 

 Thus the two corresponding areas are comparable, whatever subsequent changes take 

 place in the area of the expeiimental half-leaf. 



The Stamp.— 1 have used stamps of special design cast in rubber in the same way as 

 ordinary endorsing stamps. Each makes an impression of a rectangle bounded by lines 

 as fine and straight as possible. Surrounding this rectangle closely is another, bounded 

 by lines about a millimetre in thickness ; the broad ridge wiiich makes this outer 

 impression ser\'es the purpose of relieving the fine inner ridge from pressure, which 

 would otherwise quickly destroy it. Fig. 1 is a facsimile of an impression made by the 

 smallest stamp which I have used. The inner rectangle measures roughly 2 cm, 

 by 5 cm. 



Fig. 1. 



Besides this stamp I have used two others, making impressions which measure 

 roughly 4 cm. by 5 cm. and 8 cm. by 5 cm. respectively. 



The Mount. — The smallest stamp was mounted on a slip of plate glass, and a cork 

 attached to the other side of the glass as a handle. The other two were obtained 

 mounted like ordinary endorsing stamps.* Ordinary mounting is fairly satisfactory 

 in practice, even for so large an area as 40 sq. cm. ; but, for larger areas, it would be 

 advisable to mount the stamp in such a way that the leaf could be clamped within the 

 rectangle to be marked out, before the rubber stamp itself, which would be mounted on 

 a rectangular framework, is brought down upon it. 



Tlie Support. — Below the leaf I use a small rectangular piece of board, not much 

 larger than the stamp, covered with velveteen with a fairly thick pile. Any veins 

 which project below the leaf sink into this pile, and do not destroy the flatness of 

 the upper surface, which therefore comes closely into contact with every part of the 

 stamp. 



The Ink. — Ordinary endorsing ink absorbs water from Helianthus leaves, and ia 

 therefore unsuitable. I have used " Ardinco Never- Smear" ink, which will stand a 

 certain amount of rain, though it bleaches somewhat too readily. 



Asymmetry tests by this method, made by taking pieces from both halves of the leaves 

 at one and the same time, gave the following results : — t 



* It is advisable to select with care brass mounts with a perfectly plane surface, or to 

 have them specially worked. 



t The number of tests is small, as, owing to unfavourable conditions in the early part 

 of the summer, the supply of suitable leaves was inadequate. All the best leaves were 

 needed for assimilation experiments. 



