CHEMICAL AND PHYSIOLOGICAL STUDIES. 165 



into starch, thus :— CO^ + Hfi = CH^O + O2 (the O.^ being 

 evolved during assimilation), then BCHjO — Yi.fi = CgHj^O, 

 (starch).* At times it appears that cane-sugar may be formed 

 by the polymerisation of formaldehyde. 



The above equations, however, are by no means a complete 

 representation of starch-formation, it being probable that other 

 intermediate stages occur. Moreover, it appears that sugar is 

 the carbon-compound formed as the final product, the starch 

 being produced subsequently by a process of secretion and 

 stored in the chloroplast, and the sugar first formed may be 

 either cane-sugar or a hexose {i.e., dextrose). Some of the 

 sugar is used up at once for formative purposes, and it is the 

 remainder that is stored. In some cases, it seems that the proto- 

 plasm may be converted into starch by oxidation and splitting off 

 of the proteid and amine parts of the molecule (katabolic). In the 

 formation of the cell-plate (cellulose), some such process as this 

 appears to take place, starch or sugar being here used for 

 reconstructive purposes. The synthesis of cellulose is, however, 

 a rather more complex process than would appear from the 

 molecular composition of that substance, and the ectoplasm 

 next the cell-wall is probably here the working substance, a 

 process analogous to secretion taking place. 



The initial process, in which the chlorophyll synthesises CO., 

 and HjO to form sugar, is termed photosynthesis. The later 

 reactions involved in the production of reser^'e starch in the 

 chloroplasts are more the result of chemosynthesis. 



ii. {a) The Relation existing between Chlorophyll, Light, and 

 the Assimilation of Carbon Dioxide. (6) Pigments other than 

 chlorophyll, (c) The conditions governing chlorophyll for- 

 mation. 



(a) Chlorophyll is the green colouring matter which, as has 

 been seen, exists in the chloroplasts, probably dissolved in an 

 oily substance, which permeates the substance of these struc- 

 tures. In reality, in alcoholic solution chlorophyll is made up 

 of a mixture of two pigments — viz., a greenish one known as 

 phyllocyanin, and a yellow one, phylloxanthin.f If a leaf or other 



* See Vines, Physiology of Plants. 



t Recent researches seem to point to the fact that chlorophyll is a 

 single pigment which is readily decomposed (by alcohol or boiling water) 

 into the above-mentioned two pigments. 



