tort] CURRENT LITERATURE 309 
necessitate a modification of the current theories for the development of 
salt marshes, and lead Davis to conclude that “salt marshes in the area under 
consideration are features of and an accompaniment to coastal subsidence.” 
The rate of subsidence is variously estimated by these and other investigators 
at from rather less than one foot per century to double that amount. 
Barrett shows that a close relation exists between the chlorine content 
of the soil water and the limits of the various plant associations in the salt 
marsh. Similar data are given by HARSHBERGER® for some of the salt marshes 
of New Jersey. These are mostly formed behind barrier beaches and are of 
relatively small area. Probably the most valuable portions of this paper are 
careful plant lists and the plotting of the vegetation of various typical areas, 
which will permit further investigators to trace with exactness the develop- 
ment and succession of the various plant associations. It also affords records 
of the natural vegetation in a region where man is making such changes in the 
surface and drainage that the original plant ti idly disappearing 
Similar records are also given for certain fresh water ponds and swamps formed 
: the advance of sand dunes across the outlet of various streams.—Geo. D. 
ULLER, 
and therophytes or annuals. The flora of a region is then classified into these 
ten groups, and the number of species in each group expressed in per cent of 
the total. This numerical arrangement is called a biological spectrum. By 
arranging these spectra for different regions in order, there is given an easy 
method of comparing the life forms of vegetation, not only with each other, 
but also with the flora of the world as a whole.” From these spectra it is seen 
that the tropics are characterized by an excess of the various classes of phanero- 
phytes, deserts by chamaephytes and therophytes, the temperate zone by 
hemicryptophytes, and the arctics by hemicryptophytes and chamaephytes. 
Por the more northern floras the author finds that the number of chamaephytes 
nee 
) HARSHBERGER, Joun W., The vegetation of the salt marshes and of the salt 
and fresh water ponds of northern coastal New Jersey. Proc. Acad. Nat. Sci. Phila- 
delphia 61: 373-400. 1909 
‘* RauNKIAER, C., Statistik der Lebensformen als Grundlage fiir die biologische 
Pflanzengeographie. Beih. Bot. Centralbl. 277:171-200. 1910. 
*s Bor. Gazetre 442392. 1907. 
