SUNFLOWER LEAF 129 



The following is a convenient mode of examining the solution 

 spectroscopically : the tube of a microscope is withdrawn (this 

 may be easily done with the smaller forms of Zeiss's, Hartnack's, 

 and Crouch's microscopes), and it is replaced by a glass tube, the 

 bottom of which covers the opening of the stage of the microscope ; 

 the sides of the tube must be made opaque by wrapping round 

 them a sheet of black paper ; the solution is then poured into the 

 tube, and into the opening of the tube a microspectroscope is 

 introduced ; the mirror of the microscope is to be so inclined that 

 it reflects a beam of light on to the bottom of the tube. The 

 advantage of this method is that it enables the observer to vary 

 the thickness of the layer of the solution to be examined, and this 

 has its effect on the appearance of the spectrum, as will now be 

 shown. 



It is best to use a dilute alcoholic solution. Beginning with a 

 column of the solution about f of an inch in height, the spectrum 

 will present a single rather narrow absorption band (band I.), in 

 the red, about the line Cof the solar spectrum, extending towards 

 B ; if the height of the column be about doubled, band I. will 

 be seen to have become broader, a faint narrow band (band II.) 

 will be seen to the right of it, between the lines C and D, at the 

 beginning of the orange, another faint narrow band (band IV.) in 

 the green a little to the left of the line E t a broad faint band 

 (band V.) in the blue to the right of the line F, a still broader 

 faint band (band VI.) in the blue and indigo just to the left of 

 the line G, and finally a broad faint band (band VII. ) at the 

 extreme violet end of the spectrum. On increasing the height of 

 the column to about six inches, the bands I., II., IV. will be seen 

 to have become broader and darker, and the bands V., VI., VII. 

 to have coalesced so as completely to cut off the spectrum to the 

 right of the line F in the blue ; a new band (band III.), rather 

 broad but faint, will be seen at the junction of the yellow and of 

 the green a little to the right of the line D. 



By this means it is possible to ascertain that the spectrum of 

 chlorophyll presents seven distinct absorption bands. 



Included Starch-grains. These may be observed 

 in the cells of the mesophyll of any leaf which has 



K 



