NATURE OF PLANTS 13 



not known. It has been suggested that C0 2 and H 2 are at first 

 decomposed into simpler forms and finally re-combined into a 

 compound called formaldehyde (HCOH, written also CH 2 0). 

 This change is represented by the equation, C0 2 -|->H 2 = 

 CH 2 -f- Oo ; the two parts of oxygen passing from the cells and 

 escaping from the stomata as a gas. In the presence of certain 

 alkalies and acids, formaldehyde increases the number of ele- 

 ments which compose it, thus six times CH 2 would give 

 C 6 H 12 6 or grape sugar. This is but a theory based upon the 

 fact that C0 2 and H 2 do split up into compounds which may 

 unite to form CH 2 0. Formaldehyde can be detected in plant 

 hairs and it is possible to produce sugar from this substance by 

 treating it with alkalies and acids. All that can be definitely 

 stated about the changes going on in the leaf, during the for- 

 mation of the carbohydrates relates solely to the beginning and 

 end of the process. Water and carbon-dioxide enter the chlor- 

 enchyma cells. A series of changes follows, the nature of which 

 can only be conjectured. Finally, as the end result, sugar ap- 

 pears in the cells and oxygen is set free, escaping as a gas. 



These complex changes are brought about in the leaf in so 

 subtle a way that we are not conscious of them or of the great 

 amount of energy that is required to effect them. It requires 

 the energy expressed by a temperature of 1300 C. to decompose 

 C0 2 into its elements. Where does the plant obtain the energy 

 to bring about the decompositions and recomposition ? This 

 work is accomplished by the energy of the sunlight acting upon 

 the chloroplasts. The chloroplasts of the seed plants are minute, 

 rather lens-shaped grains, and increase in number by the division 

 of the plastid into two equal parts (Fig. 9). These bodies are 

 denser portions of the cytoplasm and like it are nearly colorless. 

 In the presence of light a green, oily substance, chlorophyll, is 

 formed in the plastids, thus producing their green color. Chloro- 

 phyll is rarely formed except in the presence of light. Plants 

 grown in cellars or in the dark are of a pale color owing to the 

 absence of chlorophyll in the plastids. Similarly green plants 

 lose their chlorophyll when placed in the dark. This is the 

 principle employed in the blanching of celery. The stalks are 



