|l6 r.,,| \\\ OF Mil- LIVING PLANT 



h until all the green pigment ha n extracted. The leaf is then 



immersion in hoi water and placed in iodine solution. It 



rill ,und that the ar< the leal which were originally green 



nnw take blue-black colour, due to the presence of starch within 



tlu . tl while the non-green parts show no such coloration. A 



mii . lamination o\ the leal would show that the starch is 



M llv deposited within the- chloroplasts (Fig. 76), while other 



ments indicate thai the oxygen of photosynthesis is liberated 



n the chloroplasl ee later). We may therefore conclude that 



tstricUd to green parts of the plant and that it proceeds 



in the chloroplasts. 



,<• chemical and physical properties of chlorophyll have been 



clog 1. Chlorophyll is a complex substance built up 



RED 



ORANGE. 



YELLOW GREEN BLUE 



VIOLET 



7000A. 



6000 & 



5000 A 



4000A. 



Fig. 77- 



rptfcn Spectrum at an ether-solution erf Chlorophyll (actually the a form). 



lack and thaded regions are respectively those in which D the light 

 r., I.t.lv or partially absorbed. The wave-lengths in Angstrom 



unr iwn below. (Re-drawn from Willstatter and Stoll, 1918.) 



a the clement- carbon, hydrogen, oxygen, nitrogen and magnesium : 

 and it is interesting to notice that it is related chemically to Haemo- 

 ibin, the red blood-pigment of mammals. The necessity of iron 

 for 1 hlorophyll formation, as already mentioned, may be due to that 

 substance acting as a catalyst in the building-up of the complex 

 molecule of the pigment. Chlorophyll can be extracted from the 

 by alchol or other organic solvents, and if such an extract is 

 I through a spectroscope it will be found that of the various 

 colours which make up sunlight, certain red rays are strongly ab- 

 sorbed by the pigment, and the blue-violet rays slightly less strongly, 

 while the intervening green and vellow rays mostly pass through 

 tbsorbed see Fig. ;;). The green leaf itself has similar absorptive 

 propertii Various experiments, some of which are mentioned 

 below, ii. that if plants nrc exposed to light of different colours, 



ynthe I rapid in the red ana (at least according to 



some m\ in the blue-violet rays: i.e. the same rays 



thai absorbed by chlorophyll. From this it may be concluded 



that chlorophyll al the particular light-rays the energy of which 



. used in photosynth* 



