HORTICULTURAL RESEARCH 491 



magnitude of the effect varies somewhat according to the variety 

 of apple dealt with but in all cases it is very great ; the effect is 

 equally or nearly as great in the case of pears, plums or 

 cherries and even in the case of forest trees, half a dozen kinds 

 of which have been investigated. Certain minor modifications 

 in the effect are noticed in some cases but it is not necessary to 

 specify these at present. 



Unless the grass be allowed to act during so long a period 

 that the tree becomes permanently stunted, the tree will recover 

 its vigour as soon as the ground is cleaned ; in the same way, a 

 limited recovery begins at once when any of the roots pass 

 outside the grassed area. On the other hand, the grass-effect is 

 noticeable when even a very small proportion of the roots are 

 in grassed ground ; for instance, when only three or four ounces 

 of the roots of trees weighing 2 cwt. are under the grass. 



It cannot be stated with certainty how far it is necessary to 

 clear the grass away from around the roots of trees so that 

 these may not be affected ; indeed, this must evidently depend 

 on the size and nature of the trees. In the case of freshly 

 planted young trees, a clear space three or four feet in 

 diameter may be advocated, though some benefit has been 

 noticed when the cleared circle was enlarged to six feet in 

 diameter ; on the other hand, benefit has been noticed even 

 when the grass was cleared away over a space extending only 

 six inches away from the stems. 



The grass seed usually sown in the experiments was a 

 mixture supposed to be suitable for orchards in the particular 

 soil in which the trials were made ; but eighteen different sorts 

 of grass have been investigated separately in experiments made 

 with trees grown in pots and all have been found to have a 

 similar effect, though generally the effect has been more marked 

 in the case of the stronger growing grasses. Clover too has as 

 great a stunting effect as grass, the only difference being that 

 the foliage of the trees is not of the light, unhealthy colour 

 characteristic of trees grown under grass ; this difference, 

 doubtless, is due to the extra nitrogen supplied through the 

 agency of the nodules on the clover roots. 



It was at first considered probable that the excessively 

 deleterious action of grass was due to its having been sown 

 around trees which had been freshly transplanted and, therefore, 

 were not established in the soil. But this was found not to be 



