194 THE FORMATION 



objects should always be taken, never the shaded one. The exposures in- 

 dicated above are based upon the smallest stop. The reasons for using this 

 whenever possible have already been given. When a larger stop is necessary, 

 the exposure is decreased to correspond; for example, a quadrat that takes 

 three to four seconds at 256 can be taken at 64 in one second. As a rule, 

 the sun should not be in front of the camera, but, when necessary, views can 

 be made in this position if the sun is prevented from shining directly into 

 the lens. 



241. Developing is as important as exposing. Indeed, it may well be 

 considered more important, since a properly exposed plate may be spoiled in 

 developing, while an under-exposure or over-exposure may be saved. 

 Owing to the ease with which plants move in the wind, the ecologist is 

 obliged to reconcile himself to many under-exposures, which can be con- 

 verted into good negatives only by skilful developing. Every base station 

 should have a good dark room, equipped with running water when possible, 

 a good ruby lantern, and the proper trays and chemicals. Prepared develop- 

 ing solutions are alluring because of their convenience, but after an extended 

 trial of several kinds, the writer has reached the conviction that pyrogallic 

 acid, or "pyro," is by far the most satisfactory in working with vegetation. 

 Of almost innumerable formulae, the following gives excellent satisfaction 

 and is convenient to use. 



L II. 



500 cc. water 500 cc. water 



30 grams sodium sulphite 5 grams pyrogallic acid 



30 grams sodium carbonate 



For developing, equal parts of I and II are mixed, and a few drops of a 

 10 per cent solution of potassium bromide added, unless there is reason 

 to suspect that the plate has been seriously underexposed. The fixing 

 bath is a concentrated solution of sodium hyposulphite, "hypo," to which 

 a few drops of acetic acid are added. It should be replaced every week or 

 two, depending upon how much it is used. A tray of water is kept at hand 

 for bringing out the detail in underexposed negatives, and a second tray 

 is used for washing. The "pyro" and the bromide solution should always 

 be within reach, the former for accelerating, and the latter for retarding 

 the development of unsatisfactory plates. 



The image will begin to show on a properly exposed plate within one 

 to three minutes after it has been put in the developer. If the image 

 appears almost instantly, and then recedes quickly, the plate is badly over- 



