BIO-DYNAMICS 113 



more growth than these did. The principal cause of this was eventually 

 traced to the fact that the soil round these trees had been heavily 

 rammed at the planting instead of being shaken over the roots and 

 merely pressed down. When we consider that the welfare of the trans- 

 planted tree depends on its sending out new rootlets from the old roots, 

 it is evident that anything which brings the soil into intimate contact 

 with these roots will be beneficial, and ramming the soil down, especi- 

 ally if it is in a wet condition at the time, will do this more effectually 

 than could ever be done by the gentler method of planting. These 

 somewhat surprising results, therefore, receive a simple explanation, 

 and it is easy to satisfy ourselves, by lifting the trees at the end of 

 a year, that the rammed trees have actually formed more new roots 

 than those carefully planted. (Italics mine.) 



The direct draft of nutrition from the soil, i.e., the 

 mineral world, which is here seen to be vitally important, is 

 what I call "cross-feeding" for the plant, and is parallel to 

 the symbiotic draft by animals on the vegetable world. 



So much in biological interpretation, in my opinion, 

 depends on this view of "cross-feeding" and its bio-economic 

 correlations, that it is worth while to show from a few other 

 instances how much is owing to this principle, and why it is 

 indispensable to the evolution of life. 



In Knowledge (May, 1914) reference is made to M. Skene's 

 investigation (New Phytologist, 1914) of some members of the 

 remarkable group of Schizomycetes, included under the name 

 of "sulphur bacteria." 



It was found that: "In mixed cultures, Amcebacter (and 

 probably also Lamprocytis) thrives best in a mineral solution 

 containing ammonium sulphate as a source of nitrogen, and 

 with chalk as a neutralising agent. All the organic sources of 

 nitrogen and carbon which were investigated proved to be 

 without favourable influence on the growth of the bacteria ; 

 indeed, as a rule they tend to inhibit development." (Italics 

 mine.) And, further, that: "Growth takes place only in 

 light." . . . "The purple sulphur bacteria require free 

 oxygen which is probably supplied in nature by associated 

 green organisms." 



These bacteria, then, are typical cross-feeders and as such 



