THE CHLOEOPHYLL APPARATUS 169 



cell-walls, and noticing the formation of starch grains in 

 the chloroplast almost as soon as the photosynthesis 

 has been established, he argues that the carbohydrate is 

 not directly formed from the simple materials absorbed, 

 but appears as a secretion product of the chloroplast. 

 He suggests that a body possibly allied to formaldehyde 

 is first formed according to Baeyer's theory, and that this 

 is used in the construction of proteid, by combining with 

 the nitrogen and sulphur absorbed in the form of salts 

 from the soil, or with nitrogenous substances derived from 

 previous decompositions of proteid. This proteid then is 

 assimilated by the protoplasm of the chloroplast, and from 

 the latter the carbohydrate (starch) is secreted. 



This view, while no doubt, in the main, accurate as far 

 as the mode 'of formation of starch is concerned, cannot be 

 regarded as explaining the formation of carbohydrates from 

 the simple compounds absorbed. The leucoplast of the 

 tuber, as well as the chloroplast itself under certain con- 

 ditions, can form starch grains when supplied with sugar 

 in the absence of carbon dioxide, and in all probability the 

 appearance of the starch is the result of the presence of an 

 excess of sugar in the leaf -cells. Regarded as an explana- 

 tion of the photosynthesis of carbohydrates, it, like the others, 

 must remain hypothetical. Moreover it is based upon the 

 assumption that starch is the highest term reached in the 

 plant in the series of carbohydrate bodies. This assump- 

 tion, however, is not supported by the evidence at our com- 

 mand, the construction of sugar and not starch being the 

 completion of the photosynthetic process of the chlorophyll 

 apparatus. Though starch is a very general accompaniment 

 to this process, it never appears till a certain amount of sugar 

 has been formed, and in many plants, particularly the 

 onion and certain other Monocotyledons, it is not produced 

 at all, however active photosynthesis may be. To this 

 point we shall return in a subsequent chapter. 



Though the production of starch is apparently not the 

 ultimate aim of the photosynthetic processes, its ready 



