56 THE MICROSCOPE. [April, 



on the edge of the cover. Draw out the water with a bit of tissue- 

 paper. The two latter media are more easily sealed in and less 

 likely to leak than the former. Chloral hydrate water, 5 grams 

 to the 1 oz., preserves the tissue well and will not shrink them ; 

 but it does not answer to mount in, if there is a chance for the 

 slide to be exposed to a freezing temperature. 



A SECTION OF ORANGE LEAF. 

 By R. H. Ward, M. D., 



TROY, N. Y. 



[From Note-book A, of the American Postal Microscopical Club.] 



This transverse section through the medium and adjacent por- 

 tions of the blade of an orange leaf contains many interesting 

 features, and it has taken the colors vividly in the double staining ; 

 but it is unfortunately so thick that its study is difficult and finally 

 disappointing in some respects. Only at one end does the section 

 taper to a little wedge thin enough to show details easily. This is 

 an excellent example of the effect so frequently and fondly de- 

 scribed, not many years ago, by the advocates of off-hand sections 

 which, being necessarily cut too thick and also uneven, were 

 believed to supply satisfactory details in the thin, wedge-like edges 

 that were almost inevitably produced by that method of slicing. 

 In this case, as usually, the thin shred at the end is so far the best 

 of the whole as to make us wish that the entire slice was equally 

 thin, and to satisfy the last unbeliever, if there is still such an one, 

 that the day of thin, machine-cut sections has fully and deservedly 

 come. 



This is a typical and very distinct example of the prevailing con- 

 stitution of leaves, which with comparatively few exceptions are 

 bilaterally symmetrical, /.<?., with the lateral halves, on each side 

 of the general axis in the centre of the midvein, essentially equal 

 and alike ; but vertically unsym metrical, the upper and the lower 

 portions not being similar halves or segments of any size, but 

 differing markedly in form and constitution, and thus giving a so- 

 called bi-facial or " dorsi-ventral " character to the leaf. 



First at the top is seen, best under the i~4th or i-5th inch, the 

 epidermis, of small, more or less tubular cells, without chloro- 

 phyll, that scarcely take a slight pink tint in the staining. That 

 portion of the walls of these cells that is exposed to the external 

 air has covered itself with a continuous filmy and colorless pellicle 

 called the cuticle, which, though an extremely delicate and trans- 



