September 12, 1901 J 



NA TURE 



495 



which is not only bathed in air, but has its microscopic in- 

 terstices permeated with it. Here, in the leaf cells, the carbon 

 dioxide of the air, which is practically an invariable quantity, 

 comes in contact with the water that has been brought from 

 the roots. Here, too, the energy of the ether waves, which we 

 call light, but which the vegetable cell recognises only as 

 force, or a mode of motion, causes the carbon dioxide to part 

 with some of its oxygen in exchange for some of the hydrogen 

 contained in the water. Thus, there is formed within the cell 

 a substance composed of carbon, hydrogen, and oxygen, the 

 exact molecular structure of which is not known ; in this 

 process some of the oxygen is freed and thrown otT by trans- 

 piration. By the introduction of the molecule of carbon dioxide 

 into the cell the equilibrium in the atmosphere of that gas is 

 disturbed and another molecule diffuses into its place ; for this 

 gas exists and behaves as if it were the only gas present in the 

 space under consideration, the same law being true for each of 

 the gaseous elements whose mixture constitutes what is called 

 the atmosphere. The consumption of carbon dioxide tends con- 

 stantly to produce a vacuum in the carbon dioxide atmosphere, 

 and the law of diffusion as constantly tends to maintain the sup- 

 ply. If molecules of hydrogen are withdrawn from the fluid 

 contents of the cell, instantly osmosis and diffusion tend to re- 

 place them ; the same is true of the solid particles in solution. 

 Assimilation within the cells of the leaves perpetually destroys 

 the equilibrium of osmotic pressure, hence this pressure creates 

 a constant flow toward the seat of demand. Evaporation from 

 the leaves, which is proportional to temperature and is acceler- 

 ated by winds, as is the supply of carbon dioxide, operates in 

 the same direction, viz. to destroy the equilibrium in the leaf 

 cells and channels, and consequently the tiny streams from the 

 rootlets are hastened onward with their precious stores of food. 

 Cold not only stiffens the sap and retards its flow, but also 

 slackens molecular motion and hinders the chemical reorgan- 

 isation of the elemenis. The process of evaporation proper is, 

 however, almost independent of the processes of nutrition, and 

 is rather a '* necessary evil." The most rapid growth frequently 

 occurs under precisely those conditions that make evaporation 

 least rapid. 



The quantity of water that passes through the plant and 

 is transpired and evaporated is enormous. The average is 

 about three hundred parts of water to one of dry matter. 

 According to experiments by Prof. King of the Wisconsin 

 Experiment Station, dent corn used three hundred and ten tons 

 and flint corn two hundred and thirty-four tons of water for each 

 ton of dry matter produced. This same experimenter supplied 

 growing corn with water as fast as it could be used to advantage, 

 and found that the crop consumed during its season of growth 

 water equivalent to a rainfall of 34 '3 inches, and yielded more 

 than four times as bountifully as a very large crop grown under 

 the best natural conditions of rainfall in Wisconsin. And he 

 concludes that " large as this movement of water is, it is seldom 

 great enough to enable a moderately fertile field to produce its 

 largest crops." And these tests in Wisconsin merely confirm 

 a conclusion that is becoming quite general, and is prompt- 

 ing the advocacy of irrigaiion even in the humid regions. 

 Moreover, the quantity of water producing a given result in- 

 creases with the fertility of the soil, and, according to WoUny, 

 the soil moisture produces its maximum results only when 

 the plants are grown in the strongest light. The value of a 

 given quantity of rainfall for the crop increases as the number 

 of rains, and what has been called the useful remainder of rain- 

 fall is only 20 per cent, of the total amount, percolation and 

 evaporation accounting for 80 per cent. Percolation is a fertile 

 source of loss of the valuable soil nitrates, especially in the wet 

 fall and winter seasons, when the corn-field is bare and a large 

 proportion of the water escapes downward. Rain, like snow, 

 is the "poor man's fertiliser," bringing down, per acre, in the 

 course of a year, at Ftothamsted, England, twenty-four pounds 

 of salt, four and a half pounds of nitrogen, eighteen pounds of 

 sulphuric acid, and much carbon dioxide, which is a valuable 

 solvent. 



Some of the less important incidental relations of climate and 

 corn, such as electricity, winds, frost, insect enemies, and 

 diseases remain to be mentioned. Electricity artificially applied 

 to the roots by charging the soil, and to the leaves by means of 

 the electric light, have both repeatedly been found 10 stimulate 

 the growth, and, in some instances, greatly to accelerate it. 

 Recent experiments show that when green leaves are exposed to 

 direct sunlight there is developed a difference of electrical 



NO. 1663, VOL. 64] 



potential between the illumined and the shaded surfaces, 

 amounting in some cases to '02 volt, but the bearing of this fact 

 upon assimilation is not well known. Atmospheric electricity 

 is a fertile source of ozone, or condensed oxygen, which is par- 

 ticularly active in the production of nitric acid. Electricity 

 stimulates protoplasm, the ultimate vital principle, and may 

 determine the character of its activities, but under natural con- 

 ditions this element is believed to have but slight influence. 



Seasonal characteristics have practical connection, too, with 

 the insect pests and diseases of corn. Not only during the 

 crop season are these pests largely at the mercy of the elements, 

 but fitful winters are sure to prove destructive to them, for 

 during the bright, warm days eggs are hatched, chrysalides 

 matured, and insects lured from their retreats, only to be caught 

 and destroyed by the sudden cold waves. The fungus diseases, 

 such as rust and smut, are carried by winds, and are favoured by 

 wet seasons, dews, and moist atmosphere. 



So sensitive is the plant to the changes of climate that even 

 the ordinary seasonal irregularities have a strong influence ; the 

 general disposition acquired by the seed in a single dry or wet, 

 warm or cold, early or late, season prepares it by virtue of that 

 experience to become the best seed for planting in anticipation of 

 another such season as that in which the seed was matured. 

 This tendency is illustrated by the well-known fact that dwarfed 

 varieties of corn from northern latitudes, when cultivated to the 

 southward, mature earlier, are hardier, and more prolific than 

 the native varieties. A corollary of great practical promise is 

 that in a region habitually or frequently dry, corn raised in the 

 driest years should be preserved for seed, as likely to be far 

 better than any that may be brought from a distance. Hence the 

 common, if not universal, practice of using seed grown in the 

 preceding year is strongly condemned. By always utilising seed 

 that has been raised in the driest years one may hope speedily 

 to develop varieties whose vegetating period will be so short 

 that the crop will rarely be injured by the hot winds of July or 

 August. And a similar rule would apply for any desired 

 disposition we may seek to impress upon the seed. 



In the light of these facts it is suggested that irrigation 

 may come to be used as a temporary device to promote the 

 evolution of new varieties that can be cultivated without irriga- 

 tion. On the other hand, recent careful work in France has 

 demonstrated that when the plants are forced to their maximum 

 yield by irrigation the seed thereby suffers a marked deteriora- 

 tion, and that for continued maximum results the seed must be 

 raised on dry soil. 



Climate being inviolable and inexorable, what hope is there 

 that the agriculturist shall be emancipated from the tyranny of 

 frost and drought ? Clearly, he must attain this by work on 

 the soil and on the plant. By utilising vast stores of energy in 

 the form of fuel man banishes the rigours of winter, thus creating 

 artificial conditions of shelter and heat, by aid of which he has 

 supplemented the process of acclimatisation. Thus, also, must 

 he cooperate with Nature in behalf of the plant : he must com- 

 bat her malignant aspects by intelligent selection ; by scientific 

 methods of culture he must supplement her beneficent efforts on 

 behalf of the human race. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Mr. J. W. BtJLLERWELL, assistant lecturer at the Durham 

 College of Science, Newcastle-on-Tyne, has been appointed 

 assistant lecturer in mathematics at the Hartley College, South- 

 ampton. 



Following the usual custom, addresses will be given at 

 many of the metropolitan and provincial medical schools, at the 

 opening of the new session early in October. At S'. George's 

 Hospital an introductory address will be given by Dr. P. W. 

 Latham, of Cambridge. The first meeting of the Physical 

 Society of Guy's Hospital will be held on October 5, in the new 

 physiological theatre, when Sir Samuel Wilks, F. R.S, will 

 preside. At St. Mary's Hospital the session will begin on 

 October I with an introductory lecture by Dr. William Hill. 

 The session at the Middlesex Hospital will .also begin on 

 October i, when Mr. T. H. Kellock will give an introductory 

 address. The session of the Faculty of Medicine of University 

 College will be opened with an introductory lecture by Prof. 

 J. Risien Russell. The session of the London (Royal Free 

 Hospital) School of Medicine for Women will be opened with 



