. A laboratory course in plant physiology. Plant physiology; Plant ecology. PHOTOSYNTHESIS 93 The cutter works on the principle of a punch (Fig. 20). A stiff iron frame, of a form conveniently grasped by one hand, carries steel dies operated by pressure of the thumb. The dies cut discs cleanly from a leaf held between them, the discs then dropping into a perforated aluminum cup screwed below the lower die. The diameter of the punch-dies is as nearly as possible cm., and hence every disc is 1 sq. cm. in area. In use the arms of the frame are slipped above and below the leaf, which is guid
. A laboratory course in plant physiology. Plant physiology; Plant ecology. PHOTOSYNTHESIS 93 The cutter works on the principle of a punch (Fig. 20). A stiff iron frame, of a form conveniently grasped by one hand, carries steel dies operated by pressure of the thumb. The dies cut discs cleanly from a leaf held between them, the discs then dropping into a perforated aluminum cup screwed below the lower die. The diameter of the punch-dies is as nearly as possible cm., and hence every disc is 1 sq. cm. in area. In use the arms of the frame are slipped above and below the leaf, which is guided by the left hand, when the discs may be cut very conveniently and rapidly, in any desired number, care being taken to avoid the larger veins. The cup is then unscrewed and covered by its own screw cap, which projects sufficiently to allow the cup to. Fig. 20.—Leaf-area cutter, with disc cups; X|. On the left is a cup in a test-tube as arranged for steaming the discs. hang near the top of an ordinary test-tube, as shown in the figure. Water in the bottom of the test-tube is then boiled in the gas-flame (any convenient holder being used), and the steam enters the perforations of the cup and kills the living cells of the discs, thus preventing any loss of weight by respiration. The cup, with its contents, is then placed in the drying-oven. After a pre- determined interval, using the other cup, an equal number of discs is cut from the same leaves. These are treated as in the first series, and the cup is placed beside the first in the drying-oven. When the discs are thoroughly dry, which -requires two or three days, both cups are carefully weighed; then the weights of the cups (stamped upon them, together with the letters M and N respectively to distinguish morning and night cups) are subtracted, when the remainder gives the dry weights. Both cutter and cups should often be cleaned, to prevent rusting of the one and accumulation of dry sap. Please note that these images are ext
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