. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . o spread them out between glassslides, and then, by holding them up to the light, all thechief characters, including the venation, can commonlybe discerned, and especially if a hand lens be employed;it is commonly necessary, however, to proceed to a lowpower of the microscope before a definite conclusion canbe arrived at. 390 LABORATORY WORK. The characters of the tea leaf, when thus examined,are these :—the shape is elHptical,
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . o spread them out between glassslides, and then, by holding them up to the light, all thechief characters, including the venation, can commonlybe discerned, and especially if a hand lens be employed;it is commonly necessary, however, to proceed to a lowpower of the microscope before a definite conclusion canbe arrived at. 390 LABORATORY WORK. The characters of the tea leaf, when thus examined,are these :—the shape is elHptical, and though its lengthmay be as much as five inches, it averages from aboutone to two inches in length, and in breadth from half toone ; the margin of the leaf shows distinct serrations,each of which is surmounted by a small spine, and theseserrations do not quite extend to the point of attach-ment of the stalk ; the apex is slightly emarginate ; theprimary veins come off somewhat dichrotomously fromthe midrib, and then branching off, form a markedlylooped network extending to near the margin of the leaf,where, by bending back, they leave a narrow clear Fig. 95.—The epidermis of the under surface of the Tea-leaf. (X285). Under the microscope the leaf shows an epidermic layerof flattened cells possessing well marked sinuous out-lines, coming off from a few of which are long slenderunicellular hairs. On the under surface of the leaf thereare a great number of oval stomates visible (fig. 95). The most distinguishing characteristics of the tea leafare :—the spine mounted serrations, which terminate alittle before the point of attachment of the stalk; thelooped venation ; the notched apex; the long slenderunicellular hairs ; and the large number of stomata uponits under surface. , TEA. 391 The leaves of the elder, willow, and sloe, are shownside by side on pages 388 and 389, in order that they maybe more readily compared ; the difference will be seen tobe so slight that
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