292 



Harris M. Benedict 



These vines were numbered, and their relative ages were obtained by 

 sawing out a thin sKce from one side at the base of the stem. For com- 

 parative purposes ten leaves were collected from each vine, as well as 

 cuttings and*material for permanent mounts. Care was taken in selecting 

 the leaves to get only fully matured, healthy, normal specunens. Since 

 conditions of humidity and temperature are different at different levels 

 above the ground, the leaves were taken from the lower parts of the 

 vines, not above eight feet from the ground. The effect of light exposure 

 has been shown by Schuster (1908) to" be a definite one, and care was 



taken that all selected leaves were such 

 as had full exposure to the sky, of the 

 same character for each of the paired 

 vines. 



The collected leaves were taken im- 

 mediately to the laboratory, measured 

 as to length, breadth, and area, and 

 weighed. The venation was then photo- 

 graphed in the following way : A heavy 

 black paper was pasted to a clean glass 

 plate, four by five inches in size. Ten 

 openings, approximately four by ten 

 millimeters in size, were then cut in 

 T? KQ 13 4 f 41, 1 ^ ^ e I. , the black paper. From the same part 



J^iG. oo. — r art oj the Lea] removed for -photo- . . : 



graphing of each leaf (Fig. 53) pieces a Uttle 



larger than the openings were cut, and 

 these were laid over the openings, so that each of the ten leaves was 

 represented. A clear glass plate was then laid over all, and the whole 

 was bound together by elastic bands, placed in the negative holder 

 of an enlarging camera, and photographed at an enlargement of three 

 diameters. Negatives showing the veinlets clearly were obtained after 

 some practice, and from these negatives velox prints were made. 



The appearance of a leaf, viewed by transmitted light, is as a vast 

 number of aggregations of photosynthetically active cells, occupying the 

 meshes of the network of veinlets. The size of these aggregations seems 

 to the writer to be of more direct physiological significance than the 

 arbitrary standard introduced by Zalenski — the combined length of 

 the veins in one square millimeter of leaf surface — and therefore 



