loS PLANT PHYSIOLOGY. 



Colored glass is most convenient for this experiment, but none is 

 obtainable in which the colors are spectroscopically pure. Gelatine 

 plates are better (see earlier, page 89), and of course must be used 

 attached to glass. But very much better results may be obtained 



Fn;. 26. GERMINATION APPARATUS AUTOMATICALLY WATERED. 



One-fourth the true size. 



by use of pure-color chambers constructed thus (Fig. 27): Take five 

 Soykas flasks, which have their faces ground and polished flat, and 

 fill them with five colors thus: white, obtained with distilled water 

 black, obtained with distilled water and India ink; red, obtained by 

 the dye " scarlet "; blue, with ammoniacal copper sulphate; green 

 by a mixture of potassium chromate and ammoniacal copper sul- 

 phate (the latter with an excess of ammonia). In the three latter 

 cases the mixtures must be tested in each flask with the spectroscope, 

 and made of just such a density that they cut out all colors but 

 their own, but the least possible of the latter. Thus adjusted, 

 loss by absorption and reflection being about equal in the three, the 

 proportional intensity of the three colors transmitted by the flasks 

 must be about as in sunlight. The rounded edges of the flasks should 

 be blackened (with black paint) to prevent light passing through 

 them. Select now an eight-inch porous earthenware pan or flower-pot 

 (see Fig. 27) ; cut a round glass plate just covering it. Cut from 

 the felt paper used in herbaria two circles the size of the glass, and 

 from these cut five circles equidistant from one another, a little 

 smaller than the Soyka flasks. Glue these papers with the circles 



