8o 



PLANT PHYSIOLOGY 



examine its color, both by transmitted and reflected light; (6) exam- 

 ine its fluorescence, which may be greatly heightened by focusing light 



into its interior with a lens; (c) examine 

 the effect of its continued exposure to 

 bright light, for which purpose it is 

 better to divide a fresh solution into two 

 equal parts kept side by side, one in 

 light and the other in darkness; (d) 

 describe these phenomena clearly, with 

 such explanation of them as you can 

 ~t gather. 



Precautions. Care must be taken 

 that the flame does not reach the inflam- 

 mable alcohol or its vapor; to guard against 

 which it is better not to attempt to heat 

 the test-tube without the water-bath. A 

 good water-bath may be extemporized from 

 a beaker of water placed on an asbestos 

 wire support over a Bunsen or spirit flame. 

 A very efficient arrangement is shown by 

 the accompanying figure 14. Or, if . there 

 is no haste, the dish may simply be stood 

 on a radiator or other warm place, when 

 the color will come out in an hour or two. 

 Some leaves (not those mentioned below) 

 do not release the color readily unless they 

 are first boiled in water for a minute or 

 two, but it is much better to omit the 

 boiling, which causes chemical changes, 

 whenever possible. Since the chlorophyl 

 decomposes in light, it must be extracted 

 under a cover, or at least not in bright 

 light. The solution can be made stronger 

 by use of more leaf, though it is apt not 

 to be clear unless filtered. Solutions thus 

 obtained are as good for study as those 

 made by the very elaborate method of 

 Detmer, 21. 



Materials. The best materials for 



Fig. 14. — Efficient arrangement 



FOR PREPARATION OF ALCOHOLIC 



„„ r „„„„„„„ . this study are given in Miss Eckerson S 



SOLUTIONS OF CHLOROPHYL; , , , , . , 



, paper upon chlorophyl spectra, cited on 



! , . . , „ . page 82. Thin, clear-green, half-mature 



The test-tube stands in a conical flask f ° . , ° ' 



covered by a tin hood. leaves are ln general the best; especially 



good are String Bean, Abutilon, Primula 



obconica, Squash, Grasses, Garden Nasturtium. Some common leaves, 



however, especially those of a yellowish-green color, such as Pelargonium 



