45 

 GRASS AND FRUIT TREES. 



The third report on the Woburn Experimental Fruit Farm, recently- 

 issued by the Duke of Bedford and Mr Spencer Pickering, F.R.S., is 

 devoted to a discussion of the effects of gr;iss on apple trees. In 

 previous reports it was shown that grasses prove most injurious to 

 young apple trees, and the experiments described here were designed 

 to throw light on the causes of injury. Up to the present time the 

 cause, or causes, have not been discovered, but the experiments have 

 made considerable progress, for they have shown that their first 

 suspicious were unfounded. Grasses might reasonably be expected to 

 injure young fruit trees by interfering with their air, or water, or food 

 supply, but the careful experiments recorde 1 in the report indicate that 

 interference ^\ith air, water, and food has little or noting to do with 

 the question, and that the injury ' must in all probability, be attribut- 

 ed to the action of some product, direct or indirect, of grass growth 

 which exercises an actively poisonous effect on the roots of the tree." 

 This conclusion is based partly on the negative evidence of the experi- 

 ments, in which the supplies of food, air, and water were controlled, 

 and panly on the appearance of the trees grown in grass. These trees 

 were always very sharply marked off from the others by peculiar tints 

 of leaf and fruit, quite unlike those due to starvation, and produced 

 obviovslv by some unhealth}' condition of soil. The effects of grass on 

 apple trees have been studied only on the shallow clay soil of the 

 Woburn Fruit Farm and on a clay soil at Harpenden, and it is possibie, 

 as the experimenters are careful to point out, that on a richer soil, and 

 in a different climate, grass might not prove iujuiious, but the 

 Woburn experiments clearly indicate that horticulturists should avoid 

 planting apples in grass, unless there is' local evidence that grass does 

 not injure the young tres. 



In their work on apple trees the Duke of Bedford and M'. Pickering 

 are dealing with a special and well marked case of a general problem 

 of great interest to agriculturists — the effects of crops and of crop 

 residues on the quality of soil. Every observant cultivator knows that 

 land may get " sick" or " over-cropped" when a plant is grown too 

 often, and he also finds that certain plants " exhaust" the soil in a 

 peculiar degree for certain other plants. He has been told that this is 

 a "food" or a "special food" question, and that interference with the 

 air, food, and water supply explains all the ills which plants may 

 suffer from competition with their fellows. At the same time, he does 

 not feel satisfied that such phenomena as the disappearance of clover 

 from land, <>r the effec's of rye-grass on wheat ate due to straight- 

 forward competition, and the "poison" theory of the Woburn experi- 

 menters will arrest his attention. Seventy years ago agriculturists were 

 discussing De Candolle's " excretory theory," and found in it the chief 

 explanation of the benefits due to a rotation of crops ; when the theory 

 was abandoned, the facts irom which it originated were forgotten, and 

 in connection with the effects of grass roots on apple trees, the follow- 

 ing sentenced from De OandoUe is worth recalling: — Thus we know 

 that the thistle is injurious to oats, the Euphorbia and Scabiosa to fl ix, 

 the Inula betulina to the carrot, the Erigeron acre and tares to wheat, 

 &c." Though the plant does not " excrete," it may readily influence 



