268 SCIENCE AND FRUIT GROWING 



a difference in the susceptibility of apples and pears to grass 

 in so far as the results with one variety of each could justify 

 any conclusion the apples suffering a reduction in vigour about 

 twice as great as did the pears (XIII, 90), so that the evidence 

 as to variation in the effect in the case of different kinds of fruit 

 trees is somewhat uncertain. 



Observations on the effect of grass on trees were extended to 

 six varieties of forest trees grown, both at the Fruit Farm, and 

 in the more congenial sandy soil at Millbrook (XIII, 40) ; the 

 results of three years' observation, based on the length of new 

 wood formed, gave 



Values compared with ungrassed trees = TOO. 

 Length of new wood. 



Millbrook. 



58] 

 48 . . 88 75 



53 



The conifers at Millbrook were less affected than the other 

 trees, and these, again, show considerably less effect than the fruit 

 trees do, the weight of prunings in the latter case (p. 20) being 

 the feature which has to be compared with the length of new 

 wood measured in the case of the forest trees (III, 40). The 

 comparatively small effect of grass on conifers in a sandy soil 

 was further emphasised by clearing the grass away from part 

 of an already established plantation of firs and larch ; the effect 

 of the clearance was beneficial, but only to the extent of 8 per 

 cent. (XIII, 30). Subsequent results, however (p. 308), have 

 indicated that the smallness of the effect of grass on conifers in 

 this sandy soil, was due, more to the action of such soil in facili- 

 tating the removal of the toxic products of the grass, than to 

 any want of susceptibility of the conifers to the toxin. 



The next point examined was whether the action varied with 

 the nature of the grass ; and experiments on the subject were 

 carried out on young apple trees grown in earthenware pots for 

 three years. Sixteen different grasses, two mixtures of grasses, 

 and two clovers were used. The general results indicated that 

 the extent of the effect was not dependent on any factor other 

 than the vigour of growth of the grass, the vigour of the tree being 



