256 
ON STARCH. 
ON STARCH.* 
BY EDWARD FRANCIS, F.C.S. 
The substance of plants is not homogeneous, but is com¬ 
posed of small structures termed cells. Each cell is a whole 
complete in itself, at least for a time, and is composed of 
solid, soft, and fluid layers. The formative material which 
closely lines the walls of the cells, and which is soft and 
inelastic, was termed by Mold, in 1846, protoplasm. It is 
an albuminous matter, and consists of protein compounds, 
fat, mineral salts, and water. It dissolves in dilute caustic 
potash, from which solution casein may be separated by 
acetic acid. This substance is analogous to the fibrin of 
animals and the gluten of vegetables. The cell wall con¬ 
sists of cellulose, one of the many liydro-carbons. The 
protoplasm encloses cavities which are filled with a watery 
fluid termed cell-sap. In all the cells of the higher plants 
the protoplasm encloses a rounded body, the substance of 
which is similar to that of the protoplasm itself. This body 
is the nucleus. By the formation of grains of chlorophyll 
the protoplasm becomes differentiated into a colourless, 
homogeneous part, and into smaller distinct green portions 
imbedded in the former, the grains of chlorophyll. This 
differentiation may take place in the dark, when yellow grains 
only are produced; but, on the contrary, the chemical process 
by which the green colour is produced has a complicated 
dependence on light. The yellow and orange rays cause the 
greatest amount of assimilation, and the violet and indigo 
least. 
The assimilation of plants depends upon the decomposition 
of carbon di-oxide by the chlorophyll of the cells, which 
process is rendered perceptible by the exhalation of oxygen in 
volume nearly equal to that of the carbon di-oxide absorbed. 
The yellow chlorophyll grains formed in the dark are small, 
but become considerably longer and green on exposure to 
light. It is only after they have assumed this green colour 
and under the continued action of light that they form starch, 
which becomes imbedded in the chlorophyll grains. This 
change may be represented by the equation— 
6C0 2 -f- 5H 2 0 = C 6 H 10 O 6 -f- 60 2 . 
From which it is seen that twelve] volumes of carbon dioxide 
produce twelve of free oxygen gas. When cells whose 
* Read before the Nottingham Naturalists’ Society, February 3rd, 
1885. 
