66 EXPERIMENTS IN BLUEBERRY CULTURE. 



appreciated until the best culture from the 1908 seedlings had re- 

 mained almost stagnant in 4-incli pais for over a month. The con- 

 dition of the plants was first attributed to an excess of acidity in 

 some of the peat used for potting, and next to the necessity of a 

 period of rest from active growth. Neither of these reasons, how- 

 ever, it was ascertained from observation of other cultures, could 

 account except in part for the distressed condition that these plants 

 finally reached. 



When one of the plants was knocked out of its pot it was in- 

 variably found that a large part of the roots at the sides of the 

 earth ball were dead. It was at the period of the year, April and 

 May, when the advent of warm sunny days made the control of 

 temperature in the greenhouse somewhat difficult, and this, together 

 with the previous rapid growth of the plants and the consequent 

 increase of their water consumption, had brought about considerable 

 irregularity in the moisture content of the pots. The conclusion was 

 reached that the walls of the j^ots had become dry on one or more 

 occasions, and that this had killed the delicate roots that came in 

 contact with them. The roots of the blueberry, as described on 

 page 42, are exceedingly slender, the smallest being about two- 

 thousandths of an inch in diameter. They are very quickly killed 

 by drying. 



On the basis of this conclusion the general practice of plunging 

 blueberry pots was adopted. If the plants are to be exposed to a 

 very warm, dry atmosphere the plunging should be done before any 

 considerable quantity of roots has groAvn through the soil to the wall 

 of the pot. It is probably still better to do the plunging imme- 

 diately after the potting, for then uniform moisture conditions can 

 be secured throughout the soil in the pot. 



Besides the avoidance of injury to the plants by the drying of their 

 roots, the practice of plunging has another marked advantage, the 

 maintenance of a moderate but adequate and even optimum degree of 

 moisture in the soil with infrequent waterings. A series of pots 

 plunged in live sphagnum in a cool greenhouse during the winter of 

 1908-9 frequently went for a week at a time without requiring water 

 and then most of the water was applied between instead of in the pots. 

 The moisture evidently moves freely in or out through the wall of 

 the pot, which is of cour.se not glazed, and an excess or deficiency in 

 any one place is soon adjusted. 



Sand has been found a convenient and satisfactory plunging ma- 

 terial. The surface of the sand should come to the same level as the 

 soil in the pot, or a little above it. A little sand on the surface of the 

 soil does no harm, and indeed is probably advantageous. AVlien a 

 single pot is to be plunged it may be done by placing it within another 



193 



