THE HOIJ-: OF r.REF^.N PLVNTS 257 



Rays of greater and shorter length are also found at eaeh end of the 

 spectrum forming the ultraviolet and infrared portions. The heat 

 of light rays varies, Ijcing greater at the r(>d end of the spectrum. 

 Since all life depends upon this I'adiant energy whose source is the 



1 z ^ 4 I n m EA 



When a green leaf is placed in the path of light passing through a {)risni. dark 

 strips appear, due to the partial or conipleh^ blocking of the light energy. These 

 are shown in the absorption spectra above. .4, chlorophyll of Alliumiirsi- 

 mim in alcohol; B, chlorophyll of English ivy {Iledera helix) in alcohol; 

 C, chlorophyll of OscUlatoria in alcohol; D, carotin. 1, 2, 3, 4. absorption bands 

 of chlorophyll; /, //, III. absorption bands of carotin; EA, end absorption. 

 The lettered broken lines mark the position of the principal absorption hnes of the 

 solar spectrum (Fraunhofer lines); the numbered solid lines form a scale from 

 which wave lengths (X) in nullionths of a millimeter may be found by adding 

 a cipher; note the increasing dispersion from left (red) 1o right (violet). 

 (After Kohl.) 



sun, the green plant is no exception to this rule. Certain parts of 

 the plant, however, are more susceptii)le than other portions to ra- 

 diant energy. While the green leaf as a whole needs sunlight, it is 

 only chlorophyll in the chloroplasts that is al:)le to utilize it for food 

 making. 



If a chloroplast is examined under a very high magnification of the 

 microscope, it is found to be a mass of living matter somewhat 

 denser than the protoplasm surrounding it. In its disk-shaped struc- 

 ture the green coloring matter is arranged around the outer part of 

 the chloroplast, while the central portion usually contains a clear area 



