September 12, 1901] 



NA TURE 



493 



the internal strains of iron and steel and their bearing upon 

 fracture. 



The object of the paper was to assist the elucidation of some 

 of the mysteries attendant upon the physical behaviour of metals 

 generally, and of iron and steel in particular, and to throw light 

 upon the cause of the sudden and unexpected breakages of metal 

 used for machinery and other purposes. Its reasonings were 

 based upon the following facts and hypotheses ; — -That there are 

 two kinds of equilibrium to which a metal attains, viz., chemi- 

 cal and physical ; that the natural tendency of a complex metal 

 is to assume its most simple forms of combination preferentially 

 capable of existing at a given temperature ; that its rapidity of 

 cooling, even under the slowest conditions, is too great to allow 

 this to reach finality ; that the equilibrium is further repeatedly 

 interfered with by changes of atmospheric and other conditions ; 

 that the adjustment to physical equilibrium tends to assist the 

 adjustment to chemical equilibrium ; that adjustment which is 

 assisted by slightly raised temperatures, also, as a consequence, 

 takes place in the cold ; and that the eutectic is the medium 

 through which the chemical or molecular change takes place, 

 working, of course, in conjunction with the vibration of the 

 molecules. 



RELATIONS BETWEEN CLIMATE AND 

 CROPS.^ 

 'T'HE weather exerts a tacit, though relentless, tyranny over 

 the labour and the thought of the agriculturist. The 

 probable influences of the present and prospective weather upon 

 the growing crops are seldom absent from his mind. But 

 science teaches that climate is rhythmic, not capricious. Laplace 

 has shown that the mean temperature of the mass of the earth 

 cannot have changed in any appreciable measure during the 

 entire period of astronomical calculation, and that while the 

 planetary movements remain as at present no such change can 

 occur. " Astronomical permanency," he says, " implies an 

 absolute fixedness of the quantity of heat for the mass of the 

 earth." And the sun's heat is the leading element of climate ; 

 all other conditions depend in the long run upon that. Hence, 

 the sun's heat being constant, all the changes we observe are 

 periodic as regards the astronomical units, the day and the year; 

 and non-periodic in all other cases, the averages returning 

 always to a line of absolute permanency. 



Climate is the average of seasonal atmospheric conditions, 

 and as corn is an annual plant, these fluctuating seasonal 

 factors must affect its growth. The crop season is in fact the 

 climatic unit with respect to this cereal. No season exactly 

 repeats itself ; there are perturbations within relatively narrow 

 limits ; the plant strives perpetually to adjust itself to perfect 

 correspondence with its environment. As this environment — 

 that is, climate and food supply — vibrates now one way, now 

 another, about a fixed mean, the consequent variations of the 

 plant will be compensatory, and so there should be no final 

 permanent modification of the plant in a given locality. 



Aside from its direct control of the amount and quality of 

 the crop, climatic variations, by vitiating experience, impede 

 agricultural progress. This fact is most apparent in the agri- 

 cultural history of a new country, where experience acquired in 

 one district is in many cases not only useless, but positively 

 pernicious, when applied to a distant district. In the United 

 States millions of dollars have been lost through the eff'orts of 

 new settlers to learn by experience the climatic peculiarities of 

 their adopted home. It is the province of agricultural science 

 to teach how to profit by the experience that has been so dearly 

 bought in the past. 



Agricultural climatology considers the relations between the 

 meteorological elements measured in terms of plant develop- 

 ment. As intimate as these relations are known to be, and as 

 interesting and promising a field as their study is known to 

 offer, it is rather surprising that no adequate organised effort 

 has yet been expended in this direction. But we are coming 

 to see that the very fact of this intimate reciprocal dependence 

 may be turned to advantage, and that by methods of correlation 

 the facts of each science may be made to illumine the other. 



The laws of biological and of meteorological phenomena 

 separately considered are extremely subtle and complex, and 



NO. 1663, VOL. 64] 



any attempt to study them in their manifold reciprocal relations 

 is sufficiently difficult to deter any but the best equipped and 

 most zealous students. This difficulty of properly interpreting 

 the separate effects upon vegetation of he.at, light, moisture, and 

 the gases of the atmosphere is enhanced by the fact that a 

 change in one meteorological condition ordinarily disturbs all 

 the other elements. For example, rain is accompanied by 

 cloudiness, decrease in light and heat, and, it may be, by an 

 increase of warmth in the soil, if the rain be a warm one. 



Extended and elaborate meteorological observations have 

 been conducted in the United States and in Europe, but instru- 

 ments measure only detached elements of climate ; plants 

 alone record its composite or cumulative effects. Hence, the 

 insistence on the part of leading agricultural investigators that 

 climate should be studied in terms of plant life. Such study 

 is termed phenology, and while it has led to some valuable 

 generalisations, the fragmentary character of the data vitiates 

 many of its conclusions. It appears that in the past pheno- 

 logists have given the element of heat undue, if not almost 

 exclusive, weight. It is becoming more and more evident 

 that the real function and value of light have been neglected 

 and undervalued. A fundamental theory which has been held 

 by botanists for more than a century is, briefly, that a certain 

 life event takes place in any species whenever that species 

 has been exposed to a certain sum total of heat, which is called 

 the physiological constant or thermal constant. In harmony 

 with this theory, Blodgett, in his " Climatology of the 

 United States," says with regard to corn that its period of 

 growth is precisely proportional to the abruptness of the 

 temperature curve ; that its unusual elasticity of constitution 

 admits it to all regions where the temperalure reaches a 

 certain point, however brief the duration of this warm period 

 may be. He defines the extreme northern limits of 

 Indian corn as coincident with the isotherm of 67° for 

 July, though a somewhat higher mean for one summer month is 

 required, and he attributes the increase of productiveness at the 

 north mainly to " the hasty growth, the excess of heat while it 

 lasts, and the hastened ripening period." The seemingly in- 

 significant item of a deficiency of two degrees on the mean of a 

 single summer month practically excludes this crop from the 

 British Isles, where it is grown, when grown at all, only as a 

 forage crop, seldom maturing any grain. This statement of the 

 subject has been for fifty years the popular and the current 

 theory. Temperature being the most easily measured of the 

 solar manifestations, it has quite naturally been regarded as the 

 dominant one. Then, too, the rudimentary state of climatology 

 made necessary such a simplification as is afforded by the 

 consideration of heat alone. 



The trend of recent opinion is summarised by Prof. Abbe in 

 his extensive manuscript report of June 1891, on the " Relations 

 of Climate and Crops," where, after reviewing the investigations 

 of Tisserand, he concludes : — 



That the temperature of the air has apparently little to do, in 

 and of itself, with the duration of time from sowing to ripening, 

 but that this depends principally on the sunshine. The tem- 

 perature of the air controls the chemical composition of the seed, 

 but the effective sunshine seems to be the productive climatic 

 element ; it furnishes the total energy at the disposal of the 

 plant, but it is also the one least studied and understood. 



Prof. Sturtevant, of New York, from tests with 128 varieties, 

 concludes that " actinism has an influence scarcely secondary to 

 temperature." So it would seem wise in the light of recent 

 study to attribute much of the hostility of a climate like that of 

 England to the greater degree of cloudiness, and the congeni- 

 ality of the climate of the Western States to the habitually clear 

 skies of summer. 



In discussing climate and corn it will be convenient to treat 

 their relations first historically and then analytically ; a cursory 

 glance at the more evident accumulated results of climatic 

 modification and limitation will prepare the way for an outline 

 of the individual factors that constitute environment and the 

 principles that govern the life of the plant. 



The original home of corn or maize is now quite certainly 

 known to have been in Central Mexico, and hence it is the only 

 one of our cereals that is indigenous to the New World. It 

 has been so long and so thoroughly domesticated that no truly 

 wild varieties are known. In geographical range and elasticity 

 of habit it probably surpasses every other cultivated plant. 

 From its original tropical home it has spread to the temperate 

 as well as the tropical regions of the world. Introduced into 



