468 THE ANATOMY OF WOODY PLANTS 



advantageous. This is made by dissolving one ounce of Mallinck- 

 rodt or Schering pyrogallol in 150 cubic centimeters of tap water, 

 acidulated beforehand with 20 drops of nitric acid. This solution 

 should be kept in the dark room and is known as "stock pyro." 

 A second solution is made by adding to tap water 10 per cent of 

 carbonate of soda and 10 per cent of sulphite of soda, together 

 with a quarter of i per cent of bromide of potash. In this solution 

 the carbonate of soda is used (with the pyrogallol) for the purpose 

 of reducing the silver in the exposed plate. The sulphite of soda 

 prevents staining, and the bromide of potash restrains a too rapid 

 development and insures a clear image. To make the develop- 

 ing solution, dilute one volume of the "stock pyro" with nine 

 parts of water. This is solution No. I. Solution No. II is the one 

 described above containing carbonate, sulphite, and bromide. 

 Of No. I and No. II take equal parts. The developer should be 

 poured quickly and evenly over the plate and air bubbles should 

 be avoided. The time of development depends upon the nature 

 of the plate, but ordinarily the image should begin to appear in 

 from thirty to sixty seconds. Development is continued until 

 the image begins to disappear. Lantern slides and bromide prints 

 are best developed with metol, which is an organic developer of 

 German origin used almost exclusively in the manufacture of 

 moving-picture films. Its employment in this connection is suffi- 

 cient proof of its value. The developer is made by adding together 

 in the proportion of one to three the solutions described below 

 under the denominations A and B. Solution A is made by adding 

 10 per cent of caustic soda or caustic potash to distilled water. 

 Solution B consists of 10 per cent sulphite of soda, i per cent metol 

 (Metol-Hauff), and a quarter of i per cent bromide of potash in 

 distilled water. After the two solutions are mixed they may be 

 diluted with advantage by adding a third- to a half-volume of 

 tap water. Development of lantern plates and bromide paper is 

 ordinarily complete in from fifty to sixty seconds. The lantern 

 plates are best exposed in the dark room, while it is often advan- 

 tageous from the standpoint of time-saving to expose printing 

 papers to daylight. Velox papers, and in particular Glossy Velox 

 (ordinary or special depending on the vigor of the negative), may 



