36 



BOTANICAL GAZETTE 



[JULY 



patches in the sand there are cases of extreme development of small 

 rootlets with close branching. 



The development of the shoot is more or less connected with the 

 presence of these plant parts. Seedlings whose roots do not come 

 in contact with such organic matter have few and small leaves, and 

 in general it would seem that the securing of food from such organic 

 matter is essential to the development and maturity of the plant. 

 Most of the plants which have reached the shrub stage are found to 



have stems which 

 have apparently 

 come up through 

 superposed masses 

 of sand, and while 

 it has not been 

 possible to demon- 

 strate the presence 

 of organic matter 

 at the base of such 

 shrub systems, 

 such presence is 

 very strongly con- 

 noted by the ap- 

 pearance of the 

 plant and the evidence from the smaller specimens excavated. The 

 condition of the shoots with very long roots will be considered later. 

 In the sphere of inhibiting factors very little evidence was 

 observed. On account of the scattered stand the roots seldom 

 come into contact with roots of other plants, but occasionally 

 they were found exploiting bits of buried plant material in com- 

 pany with and unaffected by roots of (a) other species. In one 

 case, however (fig. 7), a P. pumila seedling had sent its roots down 

 almost into a thick mat of willow roots {h). Here there seems to 

 have been a very definite dwarfing of the root system, either from 

 the presence of injurious excretions or because of the removal of 

 water or nutrient material by the willow roots. 



The presence or absence of the water table seemed to have no 

 directive effect on the P. pumila roots; in fact several seedlings 



Fig. 6. — Primus pumila with long lateral developed 

 in contact with dead Ammophila rhizome. 



