57 

 EFFECTS OF GRASS ON FRUIT TREES. 



An abstract of an account of classical research on the subject 

 of the effects of grass on fruit trees is printed in the Agricultural 

 News for March 15 The authorities quoted are the Duke of 

 Bedford, K. G., F. R. S.. and Spencer O. Pickering, M. A., F. 

 R. S. The article says in part : 



"The action of grass on fruit trees is often so deleterious 

 that it arrests all growth, and even causes the death of the 

 tree. The action is not noticed so much when the trees become 

 grassed over gradually during the course of several years, for 

 under these surroundings they can apparently adapt themselves 

 to the altering conditions and suffer much less than when the 

 grass is actually sown over their roots. 



"It was thought some years ago that the action of the grass 

 might be explained by its affecting the aeration of the soil by 

 altering the amount of carbon-dioxide present, or by its effect 

 on soil temperature, the moisture content or mechanical condi- 

 tions. Any explanation on such grounds was found to be in- 

 adequate. 



'Tt would not be possible in the space of this article even 

 to refer to the various ingenious experiments that were con- 

 ducted in order to obtain this negative generalization. It will 

 be sufficient to proceed at once to the biological investigation of 

 the question which commenced with an examination of the effect 

 on fruit trees by heating soils — partial sterilization. Briefly, it 

 was discovered that a toxic substance is produced by heating 

 soils, which was found to be toxic toward the germination of 

 seeds as well as toward the growth of plants, retarding the germ- 

 ination and reducing the percentage of seeds which germinate. 

 After cultivation, however, the toxic substances become oxidized 

 and the soil supports growth better than when not heated. 



"Curiously enough, soil removed from grassed ground was 

 slightly more favorable toward germination than the tilled soil, 

 and it absorbed water much less readily than the neighboring 

 tilled soil. This behavior provided negative evidence in favor 

 of the production of toxic substances in grassed soils ; and strong 

 evidence of a positive character was obtained later, by causing 

 washings, from grass growing in soils on trays, to reach the 

 tree-roots with practically no exposure to the air. 



"A deleterious effect was then produced nearly if not quite as 

 great as when th.e grass was grown above the roots in the ordinary 

 wav." 



