494 



NA TURE 



[September 12, 1901 



Europe soon after the conquest ot Mexico, it finds a genial 

 home only in the warm valleys of the south and central portions 

 of that continent ; it is extensively grown in Africa, and in 

 India it thrives everywhere throughout the hill country ; it 

 appears to flourish as well in the temperate as the tropical 

 regions, and at altitudes of from sea-level to 7000 feet or more. 

 Corn is, however, as it has always been and will undoubtedly 

 remain, a distinctive and characteristic American product. It 

 is cultivated from Canada to Patagonia, over 7000 miles of 

 latitude. It has been known to ripen as far north as 63", and 

 has been found a profitable crop in latitude 51° north. In re- 

 sponse to the multifarious conditions which this great range 

 imposes, countless varielies have been developed, there being 

 more than 200 in the United States alone. 



The effects of climate on maize may be appropriately classified 

 as immediate, intermediate, and incidental. Prof. Storer has 

 tersely said that the prime object of agriculture is to collect for 

 purposes of human aggrandisement as much as may be possible 

 of the energy that comes from the sun in form of light and 

 heat. Now the working capacity of sunshine is, according to 

 Kelvin, one horse-power for every seven square feet of surlace. 

 Measured by the standards of mechanics, how inefficient and 

 wasteful an engine is our agriculture at its best. The atmo- 

 sphere is directly the source of 95 per cent, of the material in 

 the total plant and of 98 per cent, of the matter in the grain of 

 corn. The plant is an elaborate machine that absorbs and 

 transforms energy, utilising solar radiation to digest carbon 

 dioxide in the leaves and to combine into vegetable organs and 

 tissues the gases of the air with the elements supplied by the 

 soil. When we remember that the amount of energy avail- 

 able, the food supply, and, consequently, the amount of matter 

 stored, all depend directly upon meteorological conditions, we 

 realise how overwhelming is the influence of climate. 



A grain of maize once matured is as inert as a pebble until 

 heat and moisture are applied ; then a sprout and a root ap- 

 pear, each for a separate function, the one for absorbing 

 ethereal waves, the other for absorbing water. In addition to 

 heat and moisture, oxygen is absolutely essential to germi- 

 nation, as well as to all subsequent growth. The importance 

 of moisture will be appreciated when we recall that water 

 performs at least four distinct offices : first, directly as a 

 food, being united in the leaves with carbon to form the 

 carbohydrates ; second, as a solvent for the nutritive matters in 

 the soil ; third, as the vehicle which transports the soluble food 

 through the roots and stems to the leaves ; and, finally, as a 

 cooling device, since, through evaporation, water largely con- 

 trols the temperature of the plant. The " free water of vegeta- 

 tion," as it is called, or the water of the juices, comprises from 

 70 to 90 per cent, of corn in the fodder stage, while the " com- 

 bined water of vegetation," or the water that remains after the 

 plant is air-dried, is 12 per cent, in a kernel of corn. 



The immediate effects of climate will be better understood by 

 glancing first at its intermediate effects through the medium of 

 the soil and through the foodisupply. Climate originates soil and 

 all the capacities of the earth for till.age, and it is at the same 

 time more than soil or tillage. For in a truly " good year " the 

 worst tilled soil returns a more bountiful harvest than it is pos- 

 sible with all our industry to extort from the best tilled soil in a 

 " bad year." The oasis differs from the desert only in the item 

 of water supply, and a given climate does not result primarily 

 from the nature of the earth's surface ; on the contrary, that 

 surface is determined almost wholly by climate. The agencies 

 that produce, and are producing arable areas from the seem- 

 ingly impervious and indurate rocks, must continue their action 

 perennially if the soil is to maintain itself. Indeed, the reverse 

 metamorphosis is constantly at work. The greater part of 

 the known rock formations were once in the form of soil, 

 and chemical, physical, and even vital forces are continually 

 engaged in the work of rock making, as well as rock breaking, 

 so that an important office of agriculture is to oppose this cyclic 

 law of nature, and to counteract the retrogressive tendency from 

 soil to rock. 



Primarily, the soil is a reservoir of moisture and plant food ; 

 but hardly secondary is its office as a vast laboratory, wherein 

 during the warmer seasons countless complex chemical agencies 

 aad numberless microscopic organisms operate unceasingly. 

 Indeed, the relations of climate to the plant through the medium 

 of the soil are so intimate and vital that no just idea of their 

 importance can be given here. These relations may be classed 

 as physical, chemical and biological. 



NO. 1663, VOL. 64] 



The physical texture of the soil determines its conductivity 

 for heat and its content of water and air, both of which in 

 proper proportions are essential to the chemical and biological 

 functions. Moreover, the water content, through its power 

 to absorb, transform, and conserve radiant energy, controls 

 the temperature of the soil. Finally, soil temperature is far 

 more effective than the temperature of the air. Heat is well 

 known to accelerate diffusion, solution, osmotic action, and 

 evaporation. Now these physical processes are precisely those 

 that perform the chief, almost the entire work involved in plant 

 nutrition and growth. Hence, a high soil temperature is essential 

 not only for the life of the plant itself, but also for the ventila- 

 tion and the life of the soil, a healthy soil being very appro- 

 priately called a living mass. On an average 40 per cent, of 

 the radiant energy incident on the soil is absorbed, conducted 

 downward, and stored in the form of heat, 60 per cent, being 

 lost to the .soil by reflection, radiation and evaporation. 



Oxygen is as indispensable to the chemical life of the soil as it 

 is to animal life. Bolh oxygen and nitrogen are essential to the 

 biological processes, and both the chemical and biological 

 activities in the soil are as indispensable to the crop as are sun- 

 shine and showers. 



The importance of right proportions of water and air in the 

 soil is further shown by the fact that the process of decay, 

 whereby organic material is turned into humus and made avail- 

 able to the plant, cannot go on without an abundant supply of 

 oxygen. A soil that contains too much water contains too 

 little air. The ferments thrive best at a temperature of 85° to 

 95°, and when the soil contains from one-half to one-third the 

 amount of water required for saturation. The ultimate source 

 of the nitrogen found in vegetable matter is the air, and plants 

 are unable directly to utilise it in a free state. The bacteria, 

 which are chiefly concerned in maintaining the available supply 

 of nitrogen in the soil, are able to work only during the warm 

 seasons, and their activity depends directly on the temperature 

 of the soil, being a maximum at 98°. On the other hand, light 

 is inimical to the life and activity of these soil bacteria, a fact 

 that may have some bearing on the rapid growth of corn during 

 hot nights, inasmuch as the work of the micro-organisms in 

 feeding the roots is then facilitated. That corn germinates best 

 at the high temperature of 98° to 100° is, undoubtedly, due to 

 its tropical origin. For Prof. Davenport shows that the attune- 

 ment of plants to environment as regards temperature has its 

 origin, not in processes of selection, but in the modifications of 

 protoplasm by temperature itself. 



Granted that the soil is porous enough and dry enough to admit 

 the air readily, ventilation is facilitated by the unequal heating of 

 night and day, and by non-periodic temperature changes as well. 

 As the .air within the soil is heated it expands, and some of it 

 is forced downward to the deeper layers ; when it cools it con- 

 tracts, and free air is drawn into the soil. The same effect is 

 produced by barometric changes ; the passage of areas of high 

 and low pressure has been found to influence the flow of water 

 from drains to the extent of 15 per cent., thus showing an iin- 

 expected movement of air in the soil. The corn belt lies 

 entirely within the region of maximum frequency and intensity 

 of barometric oscillations in the United States. Strong, and 

 particularly gusty winds, by a measurable aspiratory action, 

 have also a significant influence on soil breathing. 



Having seen how heat, light, moisture, and the supply of 

 gases operate to control the supply of those ingredients that 

 are furnished by the soil and that constitute in the main the 

 ash of the plant, we return now to the immediate effect of these 

 elements on the vital processes and assimilation. 



While light is indispensable to the assimilation of car- 

 bon dioxide, it undoubtedly exerts a directly retarding in- 

 fluence on growth proper, or cell multiplication, but the 

 beneficial effects of the higher temperature that accom- 

 panies daylight more than counteract this. Sachs showed 

 that for many plants, when kept at a uniform temperature, 

 the rate of growth gradually increases during the night 

 and is a maximum shortly after daybreak. This effect 

 of light is opposed to the eff'ect of the diurnal temperature ; heat 

 and light increase transpiration, which means a loss of water, 

 and hence less growth. This sensitiveness and response of 

 protoplasm to light is the result of the chemical changes wrought 

 therein by the light. . . , , , , 



By osmotic action the root hairs imbibe the liquid food that 

 surrounds them ; capillary and osmotic actions carry this 

 supply to every part of the plant, to the tip of every blade, 



