150 BOTANICAL GAZETTE [AUGUST — 
The first and second sections, dealing with ecological factors and their action — 
and the communal life of organisms, are but little changed, except that they are 
brought up to date, as is true of every part of the book to a most remarkable — 
egree. Sun and shade plants are called heliophytes and sciophytes respectively, — 
and their leaves are denominated heliophylls and sciophylls. The third section — 
s 
more vital, however, involving new conceptions rather than rearrangement of 3 
material, is the new classification of plant formations. Here the author departs — 
phytes, xerophytes, and halophytes. The new conception is that there is 2 
fundamental twofold subdivision into land plants and water plants. The land — 
plants are subdivided further into twelve primary groups, thus making with the 
hydrophytes thirteen main classes of plant formations, in place of the four classes 
of previous editions. For the new classification, the author states that Dr. VAHL 
is largely responsible, and especially for those following the psammophytes, 4S 
noted below. 
In former editions it will be recalled that WARMING objected, and with good bs 
reason, to the word formation as an ecological unit, largely because of its varied 4 
use by different authors. But language is a peculiar thing, and ill-chosen words 4 
often stick. It has been so with formation, and the author now attempts 1 3 
delimit the word, regarding a formation as “a community of species, all belonging 
to definite growth forms, which have become associated together by definite a 
external characters of the habitat to which they are adapted.” ‘The chief 
of formations are microphyte, moss, herb, undershrub, shrub, and forest, and 
individual formations may be simple, compound, or mixed. An association 8 
defined as ‘‘a community of definite floristic composition within a formation, ‘7 
floristic species of a formation which is an oecological genus.” The conception 
of a formation as an ecological genus and an association as an ecological species E 
is now becoming generally accepted in principle, but this concrete statement by ee. 
the father of modern ecology should make its acceptance universal. . 
The new classification of formations, with some of the leading sub-classes 
under each, follows. 
A. Soil wet; water available. (1) Hydrophytes; subdivided into plankton 
(further split up into haloplankton, limnoplankton, and saproplankton), coe 
plankton (including the microphytes of ice and snow), hydrocharid forma 
or pleuston, the lithophilous benthos (in place-of the nereids), the benthos 
loose soil (including hot spring microphytes, sand algae, saprophytic an 
phytes, and the enhalid and limnaea formations, as in previous editions). ( 
Helophytes or swamp plants; subdivided into reed swamps and bush ee” 
B. Soil physiologically dry. (3) Oxylophytes or plants of sour (i. € 
soil, characterized largely by xeromorphy; subdivided into low moor, a 
heaths, high moors, moss and lichen heaths (or tundra), dwarf shrub bes!) 
and bushland or forest on acid soil. (4) Psychrophytes or plants of cold $0" 
