Fig. 5.—Diagrammatic View of the Process of Photo-Synthesis.
This driving off of such a large amount of oxygen, entirely against the whole tendency of that element, it is assumed, is at the expenditure of much force. The only one adequate to this work is solar energy, and this is abundantly at hand. That we need not seek further for this power is proved by many and conclusive tests. Vegetable physiologists to-day are able not only to locate the sun as the chemist, that effects the changes necessary for the production of starch, but can show in what cells and portions of those cells the forces effect the synthesis. The chlorophyll granules in the living cell are the microscopic laboratories in which a silent chemist, powerful beyond all measurements, builds out of inorganic materials the food substance of the whole world of animals and plants.
Fig. 6.—Portion of Leaf Magnified, illustrating Photo-Synthesis.
[Fig. 5] is an attempt to present the above statements as to photo-synthesis in plants in such a form that it may appeal to the eye of the reader. A bit of maple twig is shown with one leaf in position. Passing up the stem in the young wood is the crude sap from the soil to the leaf. There is a downward flow of elaborated sap in the inner bark also represented. Solar energy is indicated by the wave lines as playing upon the upper side of the leaf, while the direction of the carbon dioxide is shown by the dotted lines entering from both above and below the leaf. Water of transportation is indicated as being given off, and upon a dry, hot day this is considerable, which, as it vaporizes in the tissue, tends to keep the latter cool. Lastly, with the formation of starch there is the escape of oxygen set free from the broken molecule of carbon dioxide or water or both in the formation of the starch.
[Fig. 6] is a similar attempt to show the process of starch formation with the use of a portion of the leaf in section as it might appear under the microscope. The under portion of the leaf is seen as having openings in the skin, through which the gases and vapors pass, and the middle portion above shows the porous nature of that part that is most active in synthesis. The small oval bodies in all the cells, except those of the upper and under epidermis, represent the chlorophyll granules, the special seat of the special activities which result in the formation of the carbohydrate, familiar to all as starch. To the right is a leaf vein, through which the crude sap (c. s.) reaches the synthetic cells, and the elaborated sap (e. s.) descends to places where it is needed for growth or for storage.
With the above facts in mind, there is no wonder at the activity that may reside in a field of corn during a bright day in August. Starch is being made almost by the ton daily, and, if the conditions favor, the next month will find a rich harvest for the husbandman who has assisted in supplying the conditions for the desired output of the leading carbohydrate.
The genuine starch factories of the world are exceedingly small and equally numerous, and, with the sunlight as the active force, each green cell may contribute to the world’s gain in the food substances that enable all creatures to live and move and enjoy a fairly comfortable existence.