EXCESSIVE ACIDITY OF FRESH PEAT. 61 



pected that the sand was impure and contained lime. An exami- 

 nation of the sources of the different kinds of sand used showed 

 that lime could not have caused the trouble. Finally, however, the 

 various cultures were arranged by the dates of potting, and it was 

 then found that the purpled plants had all been potted after a 

 certain date, on which a new lot of peat had been received at the 

 greenhouses. The peat in the earlier cultures had been received 

 in June and at the time of the first transplantings had been rotting 

 for four months at a Avarm summer temperature. The seedlings 

 transplanted into this peat did not lose their tips, and growth was 

 resumed almost immediately. The peat used after the middle of 

 November Avas freshly gathered, and it was in this fresh peat that 

 the seedlings suffered as already described. It should be stated 

 here, however, that by the end of two months these seedlings, which 

 meauAvhile had been making good root growth, began to make 

 rapid top growth also and later overtook their competitors. 



Acidity tests of peat from the various cultures and in different 

 stages of decomposition showed a remarkable correlation between the 

 acidity of the peat and the behavior of the seedlings. In the fresh 

 deleterious peat the acidity was excessive, varying from 0.03 to 0.046 

 normal. In the older peat in which the plants grew well the acidity 

 was usually not in excess of 0.02 normal, in one case 0.024. Fresh 

 peat rubbed through a quarter-inch sieve and showing an acidity of 

 0.034 normal had lessened its acidity to 0.02 normal after remaining 

 in a moist well-aerated condition for three weeks in the warm air of 

 a greenhouse. In view of these facts the conclusion was reached that 

 the deleterious effect of fresh peat is due to its excessive acidity. 



In the undisturbed peat of a kalmia thicket wild blueberry plants 

 are often found growing luxuriantly. After this peat is stripped 

 from the ground it becomes injurious, as has been shown, to blue- 

 berry plants that are potted in it, this injurious quality being cor- 

 related with an excessive acidity. The question arises. What causes 

 this increase in acidity and in what particular part of the soil does 

 it reside? It was at first suspected that the excessive acidity was 

 located in the less decomposed upper layers of leaves which the roots 

 of the blueberry plants in a wild state do not reach, but which, when 

 the peat is rubbed through a sieve, go into the resulting mixture. The 

 leaf layers to which reference is here made are not the uppermost, 

 nearly dry layers a year or less old, for these are removed in gather- 

 ing the peat, but the partially rotted layers one to two years old, such 

 as those shown in Plate IV. An examination of such material showed 

 that it was not excessively acid, but came well within the range of 

 acidity beneficial to blueberry plants. 



An acidity determination was then made of the roots in the peat. 

 These are the roots, chiefly of oak and kalmia, that interlace the 



193 



