44^ PLANT TdXIX-^. 



-Ml the more were these things unknuwn and unsuspected 

 by the early farmer, as, indeed, thev are unsuspected hv the 

 more simple of our own farmers to-day. which the follt)\vin.5^ 

 will serve to illustrate. At a lecture at \\'itlsOt> ( .StormheriJ^ i 

 the writer was asked what " kracht " (virtue) the ix)tato cro].- 

 put into the s^round. it heino- common experience in the district 

 that the ^\heat cro]) which followed potatoe- was \er\- much 

 l)ettcr than the wheat crop which followed wheat or other cereal. 

 The confident replv was that tlu' " krachr "' cmi'-isted in i)lent\' 

 of hard work, a view that was readiiv accepted by the meeting-, 

 because, said the\, " we plou<4h only once for wheat, but nian\ 

 times for the i)otato, which. nuireo\er, is kept free from weecK 

 all through the season by periodic sct>fflin.s^s. If itii- were not 

 done, we should get no ])otatoes." 



\\'ith increasing knowledge theories such a^^ l)e Candolle's 

 gave way to the view that, provided all other conditions are 

 satisfactory ( \ iz.. air and moisttire >upply, root nxim. tem])era- 

 ture, etc.). the vield of cro])- is determined by the i)lant-food 

 supply. 



This \ iew ap])ears to ha\e been iniiversall\ held vuitil rather 

 more than a dozen \ear> ago, when Witney and Lamerr)n. of the 

 American Bureau of Soils, startled the world by reviving l^e 

 Candolle's hypc^thesis. They ga\e it out that the infertilitv of 

 soils could not be due to a lack of plant- food, because the soil- 

 water (on which plants feed) contained the same amount of 

 plant-food, whether the soil be a rich or a jjoor one. The\ 

 stated, moreover, that while the water extracts of good soils were 

 suitable, water culture solutions of poor >oils were not. 

 and, furthermore, that these latter proved better culture media 

 in proportion as they were diliued with distilled water. On such 

 considerations they argtted that the infertility of soils must be 

 due to the presence of toxins, and not to any stiortage of food. 

 Thus, in Farmer's Bulletin 257, Whitney stated: — 



There is aiiotlier way in which iht.- UTulity of ihc soil c.m In iii.iin- 

 tained. viz., hy arranging a sjsleni vi rotation and .^revving cacl^ year a 

 crop that is not injured hy the excreta of the preceding crop; ilien. when 

 the time coines round for the first crop to ])c planted again, llie soil lias Iiad 

 anipk- lime to dispose of the sewage re'^ulting from the growtli of the 

 plant two or three years hefore. 



The resemblance to De Landolle .- hypothesi- is verv .il)\ious. 



Again : 



I should say that the soil ought to take care of the excrenu-nt of 

 plants. Whether it does this through the agency of l)acteria. whether it 

 is due to the ahnormal absorptive power of the soil or to direct oxidation. 

 .we do not know. Take a notural soil, a prairie sod; the sauitary i-oiidi- 

 tious in that soil are almost perfect. (The italicising is the writer's.) 



Further : 



Apparently these small amounts of fertilizers which wc add to tin- 

 soil have their effect upon these toxic substances and render the s^)il sweet 

 and more healthful for growing plants. We believe that it is tlirough this 

 means that our fertilizers act rather than throtigh the supplying of plant- 

 food to the plant. 



