HORTICULTURAL RESEARCH 495 



of being cut, it would be found that it had no deleterious effect 

 on the trees. This was put to the test by making several small 

 plantations of standard apple trees in a portion of the farm which 

 had been laid down to grass several years before and penning 

 sheep on one of them. But during the two years throughout 

 which this experiment lasted, the trees thus treated suffered to 

 exactly the same extent as their neighbours in grassed land 

 where no sheep were kept. A similar experiment is now in 

 progress with fowls instead of sheep ; the results during the 

 first season have been equally negative, except, perhaps, that the 

 foliage of the trees where fowls are is somewhat darker. There 

 is one notable exception in the plantation, one of the trees show- 

 ing recovered growth : but in the case of this tree the grass 

 covering the roots has been practically eradicated by the fowls ; 

 an exception which may strictly be said to prove the rule. 



Other Suggested Explanations 



Other possible explanations have been sought in the direction 

 of alterations produced by the grass in the physical condition of 

 the soil, of alterations in aeration or the accumulation of carbon 

 dioxide, of alterations in the temperature or alkalinity and also 

 of alterations in bacterial contents. But without success. 



Mechanical analysis of grassed and tilled soil failed to reveal 

 any alteration in the distribution of the finer particles by the 

 grass such as might give rise to the clogging of the roots by 

 accumulating at the root level ; indeed, what alteration there was 

 has been in the opposite direction. The grassed soil also did not 

 appear to be alkaline and when soil was made alkaline artificially, 

 even strongly so, it did not affect the trees in the same way as 

 the grass did ; nor in the particular soil examined did it have 

 much effect on the distribution of the finer particles. 



That absence of aeration cannot be assigned as the cause 

 seems to be fairly established by experiments described in a 

 former article with trees having their roots enclosed by an iron 

 drum with a layer of cement on the top ; this boxing up of the 

 tree was found to produce no effect comparable with that of 

 grass. It was also found in this experiment that the air below 

 the cement covering contained 50 per cent, more carbon dioxide 

 than air drawn from below the surface of tilled ground and more 

 than double the percentage of that in air drawn from grassed 

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