PLANT NUTRIENTS AND THEIR ABSORPTION 125 



small) have been examined in pot experiments, they have all given very similar 

 results; and this appUes equally to cases where pure sand, with the addition of 

 artificial nutrients, has been taken as the medium of growth."'^" Evidence 

 which will serve partially to differentiate between the influence of a living plant 

 and the disintegration products of its dying roots is afforded by the following: 

 "... a quarter of an acre of land, over which some 15 apple trees, 20 years 

 of age, were distributed, was planted uniformly with Brussels sprouts; those 

 under the trees suffered to the extent of 48 per cent, in their growth; but there 

 were patches in the ground where trees had been growing until the preceding 

 winter, when they had been cut down, leaving the roots undisturbed in the soil, 

 and in these patches the sprouts did better than elsewhere to the extent of 12 

 per cent. In other parts of the ground canvas screens had been erected, at a 

 height of 6 feet above the surface, to simulate, and even exaggerate, the shading 

 of the trees, and under these the sprouts gave exactly the same values as on the 

 unshaded ground. Thus, the trees themselves materially injured the crop, 

 though the soil under the trees was more fertile than elsewhere, and though 

 the shading was inoperative."'^" 



The degree of susceptibility of the apple tree to the toxic influence of 

 some other plant is indicated by Pickering's^^'' statement that the color of 

 the fruit may be materially affected "in cases of trees weighing about 2 

 hundredweight when only 3 to 6 ounces of their roots extended into 

 grassed ground." 



Though, as stated already, data are not available for the accurate 

 •estimation of the importance of organic toxins in fruit production, the 

 limited data are very suggestive. 



In commenting upon the investigations that have just been cited and on 

 others of a similar character Alderman'' remarks: "Do they not at least open to 

 some question many of our preconceived ideas bearing upon plant growth and 

 plant nutrition? . . . Do they not raise a question as to the arrangement of 

 many crop rotations {e.g., of cover crops or other intercultures) which were 

 originally worked out with the economic convenience of the grower in view rather 

 than the growth reactions of the plants under consideration? . . . If it is true 

 in Rhode Island that onions will yield 412 bushels per acre following redtop and 

 only 13 bushels following cabbages, it is probably true elsewhere and the place 

 of the onion in the cropping system of the truck grower deserves the most serious 

 study. If grass affords direct injury to apple trees growing in shallow soils 

 underlaid with an impervious stratum of subsoil, it is probably as offensive in 

 North America as in England. The writer and others interested in plant nutri- 

 tion have repeatedly pointed out the difference in reaction to fertilizers between 

 orchards in sod and those under cultivation. It has been generally believed that 

 this difference was due to soil exhaustion of important plant food material or to 

 an influence on moisture supply but the work of Pickering is a direct challenge 

 to such a belief. Perhaps it is not important to the grower of fruit to know 

 whether an application of nitrate of soda to a sod orchard is beneficial because 

 it supplies some element of plant food material heretofore lacking or because it 



