PHOTOSYNTHESIS 81 



species and Oxalis Bowiei, yield a yellow-green and less typical solu- 

 tion. For fluorescence the best materials, in order of excellence, are 

 Jacobinia magnified (very striking), Cineraria, Oestrum elegans, and English 

 Ivy. 



ALCOHOLS. All three of the common laboratory alcohols are good for 

 this purpose. They are (i) the most-used ethyl alcohol or "spirits of wine," 

 C 2 H 6 O, boiling at 78 (costing about 90 cents a quart retail, but about 10 

 cents to institutions with tax-free privilege); (2) methyl or "wood" alcohol, 

 CH 4 O, boiling at 66 (costing about 35 cents a quart); and (3) denatured 

 alcohol, called also methylated or Columbian spirits, a mixture of the two 

 preceding (costing about 30 cents a quart). The ethyl alcohol is sold in a 

 95% strength; the strength is determined by a special specific-gravity alco- 

 holometer. In making up various strengths with water, the proper quanti- 

 ties of both must be measured out separately and then poured together, 

 since there is a shrinkage when they are mixed, resulting in erroneous volumes 

 if one is added to the other in the same measuring-glass. Alcohols are best 

 kept in glass-stoppered bottles. Upon the iodoform test for alcohol, see under 

 Fermentation later. 



DEMONSTRATION. That chlorophyl can be removed from green tissues, 

 leaving them white, may easily and strikingly be shown to an entire class as 

 follows. Prepare an arrangement like that of Fig. 14, but of the largest 

 practicable size and without the hood, which is needless away from direct sun- 

 light. Bring the water to boiling and put out the flame; take from String Bean, 

 Tropceolum, or Abutilon, an adolescent leaf with a long petiole and with a blade 

 less than half the length of the test-tube; by petiole (and forceps if neces- 

 sary) dip the leaf for a minute in the hot water, and then drop it, loosely rolled, 

 (not crumpled), into the test-tube; fill the latter two-thirds full of alcohol, 

 and insert a grooved stopper, which is to press against the petiole so that this 

 will hold the blade towards the bottom of the test-tube. Lower the test-tube 

 into the hot water, when the alcohol will soon boil, and the color will come 

 out rapidly and show very clearly, especially against a white background. 

 After it has thus boiled for five to ten minutes, pour off the alcohol and replace 

 it by water, when the leaf will show white. No doubt, if it were worth while, 

 the process could be projected upon a screen. 



The chemical and physical constitution of chlorophyl must 

 now be considered by the student. Although some of the simpler 

 phases admit of ready experimental study, the more fundamen- 

 tal matters do not, and he may best work out the subject through 

 the literature. Accordingly he should become acquainted with 

 (a) the composition, the conditions of formation (especially as 

 to light and temperature), and the stability of chlorophyl in the 

 living leaf; (b) the nature and supposed meaning of the associated 

 colors, xanthophyl, erythrophyl, etiolin, carotin; (c) variegation 

 in leaves; and (d) autumn coloration. 



