Miscellaneous. 361 



comes in contact with the roots of plants, and as they ahsorb it more 

 flows to them. The sokition of substances thus brought to the plant 

 world would seem to be a very simple thing-, and perhaps it is the 

 simplest factor in plant nutritLon, yet the nature of such solutions en- 

 gages the study of the most acute physicists and chemists, an.d can not be 

 said to be understood fully even yet. After the water has entered the root, 

 what causes it upward flow? Why does it flow downward at times in the 

 performance of its mission of transferring nutriment from one point to 

 another? Why does the plant apparently exclude some of the things in 

 solution for which it has no need, and helplessly admit others in injurious 

 quantities ? These are questions about a simple process that are yet wait- 

 ing for a complete answer. 



Water acts more than as a mere solvent ; it enters into chemical com- 

 bination. Within the cells of the leaves of plants combinations and de- 

 compositions are taking place that have thus far defied the chemist's art. 

 Carbon dioxide from the air enters, and from it and water that wonderful 

 series of compounds called the carbohydrates is built up. We are not 

 sure of even the first step in that process, though several beautiful theories 

 have been advanced and some experimental evidence adduced. We know 

 that in this wonderful laboratory oi living cells a highly complex substance, 

 starch, makes its appearance, that, in coaiipositio,n, it is equivalent to water 

 plus carbon, and that oxygen is simultaneously set free. The steps in 

 its formation are but dimly seen. We know, too, that this starch goes 

 into solution, and that starch is deposited in the grain of cereals, the 

 tubers of potatoes, and many other places where we have no reason to 

 suppose that it has been produced from carbon dioxide and water, but 

 rather from some soluble product of the starch formed in the leaves. 



W^ater and carbon dioxide do not spontaneously form starch even 

 within the cells of the plant leaves. It is only under the influence of the 

 radiations from the sun that this synthesis takes place. The sun is the 

 great motive power for earthly processes. The radiant energy which for 

 untold ages he has emitted is to a slight extent intercepted by the earth, 

 and to this can be traced the greater part of all that makes the earth what 

 it is — the winds, the rains, the flowing streams, the growing plants, and 

 hence the animals. The energy that reaches one square inch of leaf sur- 

 face in full sunlight, if entirely used in constructing starch from water 

 and carbon dioxide, which produces about one ten-thousandth of a grain 

 per second. Small as this amount is, when it is multiplied by the im- 

 mense leaf surface presented by a cornfield, it accounts for the rapid 

 growth of this plant in favorable weather. The energy of the sun is 

 often referred to as heat or light; strictly speaking it is neither. With 

 the exact nature of radiant energy we need not concern ourselves at 



