Carbon Assimilation. 
229 
capacity for forming starch, many plants not forming it all. In these 
cases it was shown that the absence of starch was not due to rapid 
translocation, for no starch was formed even under conditions most 
favourable to rapid assimilation and accumulation of products. 
The same investigator showed later (1886) that leaves depleted of 
starch floated on sugar solutions could form starch from the sugars. 
Thus almost all leaves formed starch from a 10% solution of fructose, 
a few from glucose and a very few from galactose. It became 
reasonable to suppose that starch might possibly be formed in the 
leaf from sugar. 
Confirmatory evidence of this theory was derived from 
researches on starch formation in the plant, carried out by Boehm 
(1874, 1876, 1877) and notably by Schimper (1880). Boehm showed 
that not all starch is the direct result of carbon assimilation. Thus 
he showed the formation of starch in the leaf as a result of 
transference of reserve material from other tissues under feeble 
light intensity, and in an atmosphere devoid of carbon dioxide. 
Schimper investigated the development of the starch granule. He 
showed that starch is always formed in a plastid, which might be 
colourless or green, and although he held that the mesophyll 
chloroplasts could not elaborate starch from other carbohydrates, 
further work of Boehm (1883) and that of A. Meyer mentioned above, 
showed that these chloroplasts could elaborate starch from sugars. 
These considerations lead to the conclusion that there is no difference 
between the chloroplast and the colourless amyloplast in regard to 
their powers of elaborating starch, and it is at least possible that 
starch formed normally in the chloroplast is formed secondarily and 
not as a direct result of assimilation. 
These considerations were generally held to support Baeyer’s 
theory, to which we shall refer in detail later, that the first part of 
the assimilation process consisted in the formation of formaldehyde 
which polymerised to hexose, and then gave rise to sucrose or starch. 
This theory, which involves the view of hexose as the first sugar 
formed in assimilation, has recently received support from the work 
of Strakosch (1907), who investigated the distribution of sugars in 
the leaf and other parts of the sugar beet, by means of microchemical 
tests depending on the production of osazones. He concludes 
that glucose is the only sugar present in the mesophyll cells of the 
leaf. In the veins fructose appears as well, and later, sucrose. 
Maltose also occurs only in the petiole. Strakosch therefore 
concludes that glucose is the first sugar formed in assimilation and 
