74 SCIENCE PROGRESS. 



sequent chemical analysis. Belzung describes asparagin 

 as being the form most commonly met with, though leucin 

 and tyrosin occur more frequently than has been supposed, 

 and in greater amount. In germinating seeds of Cicer 

 arietinum he detected as a normal product the body 

 xanthin, which has hitherto been held to be a product 

 of putrefactive changes where it occurs in plants. 



Of carbohydrate reserve materials the form most widely 

 distributed is that of starch. Its occurrence is almost 

 universal, nearly all plants at some time or other forming 

 it, and usually in very large amount. Its places of storage 

 cannot be enumerated, nor can any description of the 

 grains composed of it embrace every form found. Being 

 insoluble in water, and readily identified by its characteristic 

 reaction with iodine, it presents but little difficulty in its 

 detection. Wherever found it appears as grains of definite 

 shape, and these often characteristic each of its own par- 

 ticular plant. The sizes and complexity of structure of the 

 grains vary very much, even in different parts of the same 

 plant. 



It has been generally held that the appearance of starch 

 in different parts has a different meaning from the point of 

 view of the metabolism of the plant. In parts not exposed 

 to light, it has always been looked upon as a true reserve 

 material, intended for either immediate or deferred consump- 

 tion. But in leaves and other chlorophyll-containing parts a 

 different interpretation has been given. Occurring originally 

 in the interior of the chlorophyll grains, and being found 

 almost immediately upon the absorption and decomposition 

 of carbonic dioxide, it has been held to be a stage in the 

 process of construction of organic material ; indeed, it is 

 usually described as the first visible product of assimilation. 



Some investigations made by Brown and Morris (23) 

 on the metabolic changes in foliage leaves tend to disprove 

 that view, and to lead to the opinion that in leaves as else- 

 where starch grains are always the results of a process of 

 destructive metabolism, and are reserve materials, even 

 when occurring in the bodies of chlorophyll grains. The 

 experiments were made with the leaves of the garden 



