238 PENNYP ACKER— ON THE BEACH PLUM 



easily separates the two formations. At a period in the early Cenozoic, 

 when the waters of the Atlantic washed the land at a point near Clemen- 

 ton, Prunus maritima was evidently growing along the then sandy 

 shore line, but as the ocean slowly retreated eastward and time passed, 

 isolated patches of it seem to have become stranded. Further evidence 

 of this is illustrated by Stone (27) in his distribution of Prunus maritima 

 over the Pine Barren region to the east, which is geologically younger. 

 With the on-coming of the ice, and the approach of the glacial period, 

 we find that although this area was not glaciated yet the effects of the 

 period upon the plant Hfe could not have been more than to vary the 

 type, if it were permitted to live at all, and that is just exactly what I 

 have found, a variety with characters markedly different from any 

 found along the coast. Only one variety, the small blue, is found there, 

 which I have named — P. maritima var. praecox. 



5. Habitat and Environment 

 Prunus maritima is found growing most abundantly on the drifting 

 sand dune area along the Atlantic coast. At Cape May Point, where 

 I have made extensive studies of the plant, I have found it growing with- 

 in twenty-five yards of the limit of high tide. The thicket formation 

 there is rather narrow, as back of the limited sand dune area is an exten- 

 ded marsh. To the south west, however, it extends for a distance of 

 several miles, covering an area of many acres. At other places along 

 the coast, the areas are much smaller, consisting in some places of only 

 a few hundred bushes, while at Hainesport and at Atco we find isolated 

 colonies of 50 to 100 bushes. The plants of this habitat consist oiQuercus 

 falcata, Juniperus virginiana, Myrica carolinensis, Ilex opaca, Pinus 

 rigida Rhus radicans, Sassafras officinale, Solidago sempervirens, Ammo- 

 phila arenaria, Lathyrus maritimus, Hudsonia tomentosa, etc. Regarding 

 the inland distribution of the species it is quite interesting to note that 

 the blossoms appear about two weeks earlier than those of the shore 

 varieties, and the fruits are fully matured before the ones at the shore 

 have begun to ripen. This is undoubtedly due to the environmental 

 conditions under which they are growing, as it is true of many other 

 species of shore plants, that they are often retarded in their development 

 and growth in the spring by cold breezes from the ocean. Again I have 

 noted that the blossoms on the bushes nearest the ocean are the last 

 to open. Likewise, the smallest bushes bloom the earliest, and the lowest 

 blossoms open the earliest, i.e., the blossoms at the tip of the branches 

 are the last to open. The explanation obviously is the radiation of 

 heat from the sun-heated sand. 



