The Prevalence of Green Color in Plants 19 



from one side, as all plants kept in house windows attest. All 

 of these facts unite to imply an extremely close relation between 

 the meaning of chlorophyll to the plant and the action of light, 

 even suggesting, indeed, that the chlorophyll is inserted, as it 

 were,, between the light and the use thereof by the plant. To 

 this subject we shall later return, for we are dealing at present 

 with the distribution of chlorophyll in the individual plant, a 

 matter which can further be illustrated, in purely diagrammatic 

 or conventional fashion, by the picture which forms figure A of 

 Plate I of this book.* 



So important is chlorophyll, that the reader ought really to 

 make its closer acquaintance through actual experiment ; for here, 

 as everywhere else in science, an actual personal contact with 

 facts or phenomena makes all the difference in the world in the 

 clearness of one's understanding of them. It is possible to ex- 

 tract the chlorophyll very easily from leaves. If one takes two 

 or three soft thin green leaves, places them in any glass dish which 

 is uninjured by heat, covers them with alcohol (of any of the com- 

 mon kinds), and lowers the dish into hot water, then the chloro- 

 phyll will come out into the alcohol before one's very eyes. Its 

 most striking characteristic is the beautiful green color of the clear 

 solution, together with a remarkable and beautiful red fluorescence 

 which appears when the solution is held in some lights, and es- 

 pecially when sunlight is focussed upon it with a lens. And the 



* This picture is meant to represent that which one would see on a surface ex- 

 posed by a lengthwise cut through the center of such a reduced conventionalized 

 plant. Such sections, called optical sections, are very much used in biological works. 

 Thus, on the very same plate, (Plate I), appear optical sections of a piece of a leaf, 

 a single cell, and a chlorophyll grain; and a good many others occur elsewhere in 

 this book. In every case an optical section is supposed to be typical, that is, taken 

 through the part most illustrative of the structure in question; and, where only one 

 section of an object is given, it means that the object is substantially alike all around 

 the axis that is represented. Such sections, therefore, always stand for solid objects, 

 and the reader should learn, as quickly as possible, to construct the solid in his mind 

 from the section on the paper. This intellectual visualization, of course, requires 

 imagination, but that is a quality which, despite the popular belief to the contrary, 

 is highly essential to success in science. 



