igig] WATERMAN— ROOT SYSTEMS t,3 



General description of certain species. — Prunus pumila. 

 — This was the species first investigated because, as a perennial 

 well distributed over the Betsie complex, it showed promise of a 

 permanent and well marked root system. On investigation it 

 proved to have not only these features but other characteristics 

 which admirably fitted it t,o serve as a basis of comparison with 

 other species. As usually observed on the dunes, the plant has 

 more or less of a shrub habit, with many stems caused by vegetative 

 reproduction of parts buried by the sand. Under these conditions 

 it frequently functions as a sand binder and forms a protected knoll 

 or hummock. On the other hand, where the sand is being blown 

 away, a long straggling stem will be produced, more or less prostrate 

 and with little branching. In general the shrub type seems to 

 fruit best, and seedlings are most abundant at the base of a shrub or 

 around a knoll, although the fruits sometimes roll or blow some 

 distance before being covered with sand. 



The only conditions of germination seem to be burial over a 

 winter in i or 2 inches of sand. In the laboratory the seeds germi- 

 nated readily in a sterile moist chamber on filter paper, after the 

 stony pit and the seed coat had been removed. 



After 3 months' growth on the dunes the root system shows the 

 general type illustrated in fig. i, while a 3-year-old seedling is 

 shown in fig. 2. The root system, however, does not usually develop 

 along these lines. The more usual form is extremely asymmetric 

 and develops very unevenly, as indicated in fig. 3. All the seedlings 

 show wide individual diversity of form, and these specimens are 

 not at all exceptional in their eccentricity. An examination of these 

 asymmetric forms shows that their irregularities are connected with 

 the distribution of more or less decayed plant parts under the sand. 

 A typical illustration of this is shown in fig. 4, where horizontal 

 laterals are shown passing through and exploiting bits of stems, 

 branches, fete. When a seedling grows in the vicinity of a dark 

 layer already described, its laterals are generally found in these 

 layers, and they are more branched and longer than those in ordi- 

 nary dune sand; in fact, a layer of this sort will generally be found 

 to contain many rootlets of various species of plants, while the sand 

 on either side is almost completely free from them. An interesting 



