94 Plants and their Ways in South Africa 



hydrate, which will dissolve out the green colour. Leave them overnight 

 or until the green has dissolved. Boiling hastens the process. Place 

 them in a porcelain or other dish with a white bottom, and pour over 

 them a solution of iodine. The starch in the leaf will become a dark 

 blue. 



Perform the same experiment with variegated leaves of Coleus. 

 Thin leaves should be used, as the colour is dissolved more readily. 

 Starch will be found only in the green portions. In higher plants 

 chlorophyll is necessary for assimilation. 



Ex. 39. Place a potted plant {Medicago, Oxalis, and Lucerne are good 

 for the purpose) in a perfectly dark place and leave lor forty-eight hours. 

 Dissolve out the chlorophyll from the leaves and stain with iodine. They 

 remain uncoloured. The accumulated starch has been used and none has 

 been formed in darkness because the chlorophyll grains cannot appro- 

 priate the carbon contained in starch, without the energy obtained by the 

 action of the sun's rays, and so the appropriation of carbon by the plant 

 is known as photosynthesis or carbon assimilation.^ 



The photosynthetic process may take place in the follow- 

 ing manner : carbonic acid gas (CO.2) taken into the plant may 

 form a solution with the water (H.^O) which is brought up to 

 the green cells and a portion of the oxygen (O) then passes off 

 into the air, the solution deprived of its oxygen becoming 

 formaldehyde (CH2O or HCOH). Just what part the sun's 

 rays perform is not certain ; it may serve to disassociate the 

 oxygen from the carbon and hydrogen atoms. Formaldehyde 

 may be produced chemically by subjecting a solution of COg 

 in water to a weak electrical current. The sun's energy may 

 be changed in the plant to electrical energy and effect the 

 same change. 



The molecules of formaldehyde, which is found in plants in 

 small quantities, seem to be quickly grouped together in the 

 cells where it is formed. Six molecules thus grouped could 

 form grape sugar (glucose, CgH^gOg). These stages may be 

 represented by the following formula : — 



CO2 I- H^O = H2CO3 = H2CO + O2 

 6H2CO = CeH,206. 



1 The old method of covering a portion of leaf with cork or tinfoil is 

 unsatisfactory. Carbon dioxide is excluded as well as light. Prof. 

 Ganong has invented an ingenious frame which will admit air to the leaf 

 while excluding light. 



