August, 1913 THE CARDEN AND FIELD. m 



ami plants urc uu.ihlf directlv to 

 utilise it in a fm- stad-. The bai- 

 toria, whii-li arc chiolK concerned 

 in maintaining; the a\ai1.il)lo snp- 

 1)1\- (vf nitr<)>;;vii ini tho soil, are ahlo 

 to work only dnrin<^- the warm 

 seasons, and their activity depends 

 directly on, the temperature of the 

 soil. On the other hand, li<iht is 

 inimical to the life and activity of 

 these soil bacteria, a fact that 

 mav have some hearini; : on the 

 rai)id sfrowth of maize during^ hot 

 nijihts, inasinuch as tlu- work of 

 the micro-orj^anisms in feeding the 

 roots is then facilitated. That 

 maize s^erminates liest at the hi<;"h 

 temperature of 98 deijrees to 100 

 deg^rees is, iindioiibtedly, dive to its 

 tropical orig-in. 



Granted that the soil is porous 

 enoug"h and drv enou;rh to, admit 

 the air readily, ventilation is 

 facilitated bv the uneonal heatin<^- 

 of niofht gnd day, and by non- 

 periodic temperature chancres as 

 well. As the air within the soil 

 is heated it expands, and some of 

 it is forced "downward to the 

 deei>er layers ; w^hen it cools it 

 contracts, and free air is drawn 

 into the soil. 



— Vital Proces.9es. — 



Ha%nng- seen how heat, light, 

 moisture and the supiilv of gases 

 operate to control the supply of 

 those ingredients that are furnish- 

 ed bv 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. 



A^Tiile light is indispensable to 

 the assimilation of carbon dioxide, 

 it undoubtedlv exerts a directly re- 

 tarding influence on growth pro- 

 per, or cell multiplication, but the 

 beneficial effects of the higher tem- 

 perature that accompanies day- 

 light more than counteract this. 

 This sensitiveness and response of 

 protoplasm to lieht is the result 

 of the chemical changes wrought 

 therein by the light. 



— Osmotic Action. — 



Bv osmotic action the root hairs 

 imibibe the liquid food that sur- 

 roimds them ; capillary and osmo- 

 tic actions carry this supply to 

 every part of the plant, to the tip 

 of every blade, which is not only 

 bathed in air, but has its micro- 

 scopic interstices permeated with 

 it. Here, in the leaf cells, the car- 

 bon dioxide of the air, which is 

 practically an invariable quantity, 

 comes in contact with the water 



tli.it has Iwen brought from the 

 roots. ' Here, too, the energ\- of 

 the ether waves, which we lall 

 light, but which the vegi'tal)!*- cell 

 recognises only as force, or a mode 

 of motion, caiises 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 com- 

 I)osed of carbon, hydrogen and 

 oxygen, the exact molecular struc- 

 ture of which is not 'known ; in 

 this process some of the oxygen is 

 freed and thrown off bv transpira- 

 tion. AssimJlation within the cells 

 of the leaves perpetually de.stroys 

 the equilibrium of osmotic pres- 

 sure, hence this jiressure creates a 

 constant flow toward the seat of 

 demand. Kvaporation from the 

 leaves, which is jjroportional to 

 temperature and is accelerated by 

 winds, as is the supjiiy of carbon 

 dioxide, operates in the same di- 

 rection, viz., to destroy the equili- 

 bri|um in the leaf cells and chan- 

 nels, and consequently the tiny 

 streams from the rootlets are 

 hastened onward with their preci- 

 ous stores of food. Cold not onh^ 

 stiffens the sap and retards ' its 

 flow, hi'it also slackens molecular 

 motion and hinders the chemical 

 reorganisation of the elements. 

 The process of evap'oration proper 

 is, however, almost independent of 

 the processes of nutrition, and is 

 rather a " necessary evil." The 

 most rapid growth frequently oc- 

 cuTs under precisely those condi- 

 tions that make evaporation least 

 rapid. 



— Water. — 



The quantity of water that 

 passes through the plant and is 

 transpired and evaporated is enor- 

 mous. The average is about three 

 hundred parts of water to one of 

 drv matter. According to experi- 

 ments by Prof. King, of the Wis- 

 consin Experiment Station, dent 

 maize used three hundred and ten 

 tons and flint maize two hundred 

 and thirty-four tons of water for 

 each ton of dry matter produced. 

 This same experimenter supplied 

 growing maize 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 imder the best 

 natural conditions rf 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." 



— ICIlect on Sie<i. - 

 So sensitive is the plant to the 

 changes of climate that even the 

 ordinary .seasonal irreguUinties 

 have a strong influence ; the gene- 

 ral disiiosition acfjnired 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 m.aturcd. This tendency is il- 

 lustrated bv the well-known fact 

 that dwarfed varieties of maize 

 from northern latitudes, when cul- 

 tivated to the .southward, mature 

 earlier, are hardier and more pro- 

 lific than the native \-arieties. A 

 corollary of gret^t practical pro- 

 mise is that in a region habitu.-il- 

 ly or frequently dry, maize raised 

 in the driest years should be pre- 

 served for .seed, as likelv to be far 

 better than any that mav be 

 brought from a distance. Hence 

 the common, if not universal prac- 

 tice of using .seed grown in the 

 preceding year, is strongly con- 

 demned. By alwa3\s utilising seed 

 that has been raised in the driest 

 years one may hope speedily to de- 

 velop varieties who.se vegetating 

 period will be much shortened. 

 And a similar rule would applv 

 for anv desired disposition we may 

 .seek to impress upon the seed. 



In the Kght of these facts it was 

 suggested that irrigation mav 

 come to be used as a temporary 

 device to promote the evolution 

 of new varieties that can be culti- 

 vated without irrigation. 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 de- 

 terioration, and that for continued 

 maximum results the seed mvjst be 

 raised on drv soil. 



Climate being inviolable and in- 

 exorable, what hope is there that 

 the agriculturist .shall be emanci- 

 pated from, the tvra"ny of frost 

 and drouo-ht ? Clearly, he must 

 attain this bv work on the soil 

 and on the plant. Bv utilising 

 vast stores of energy in the form 

 of fj'iel man banishes the ritrours of 

 winter, thus creating artificial con- 

 ditions of shelter and heat, bv aid 

 of which he has sup])lemented the 

 process of acclimati.sation. Thus, 

 also, must he co-operate with Na- 

 ture in behalf of the plant : he 

 must combat her malignant as- 

 pects bv intelligent selection ; by 

 scientific methods of culture he 

 must supplement her beneficent ef- 

 forts on behalf of the human 

 race. — Nature. 



