382 BOTANICAL GAZETTE [MAY 
important contribution to the history of botany for a period which is compara- 
tively inaccessible to readers of English alone. One appreciates how gradually 
the science has evolved. Although the epoch-makers of the modern science were 
to come later, the roots of many of the leading principles are here disclosed. The 
style is clear and animated, requiring no needless effort to grasp the author's 
meaning. An excellent index is an additional source of satisfaction.—E. J. Hit. 
Vegetation dynamics in the desert 
There is no habitat where’ the vegetation appears more static than in the 
desert, but SPALDING? has now clearly shown that well-defined successions are to 
be found there as well as elsewhere, and that the ‘‘struggle for existence” involves 
several years of intensive study on Tumamoc Hill (the location of the Desert 
Laboratory) and the adjoining valley, and it is concluded that the distribution of 
plants in that neighborhood can be accounted for by causes now in operation. 
The first chapter considers the plant associations and habitats. The river and 
irrigating ditches are relatively poor in aquatics. The river margin is fringed 
with an association in which cott ds and willows dominate, while the mesquite 
(Prosopis velutina) is the dominating species of the floodplain; an interesting 
phenomenon in the latter habitat is the invasion of the more xerophytic Bigelovia 
Hartwegii. Salt spots are present with characteristic halophytes, but the most 
pronounced of the latter (i.e., Swaeda Moquini) grows. more luxuriantly along 
irrigating ditches than in salt spots. The washes, which are dry drainage chan- 
nels, are characterized by the palo verde (Cercidium) and catclaw (Acacia Greggit), 
while the more xerophytic slop tenanted largely by the creosote bush (Larrea 
and Franseria associations. The hill is characterized by Fouquieria and Parkin- 
sonia on any exposure, while the giant cactus (Cereus giganteus) and Encelia 
jarinosa are essentially south-slope species; Lippia Wrightii equally characterizes 
north slopes, which are also much richer in the aggregate number of species an 
individuals than are other slopes. An account of the lichens is given by FINK, 
Acarospora being th t ck teristi ; the lichens generally are unusually 
xerophytic in structure. 
The second chapter considers the detailed distribution (with maps) of aaa 
of the more characteristic species, and the third chapter has to do with environ- 
mental and historical factors. An account of the geology of the region is presented 
by Toman, and of the soils by Lrvincston. There are extensive tables depicting 
the soil moisture, rainfall, temperature, and evaporation. MacDovueat contrib: 
utes an interesting chapter on the origin of desert floras; xerophytes are regarded 
as of recent origin, and the view, formerly current, that the desert xerophytes have 
arisen through adaptation is opposed, at least as a general explanation. The 
final chapters give a review, discussion, and summary. 
2 SPALDING, VOLNEY M. Distribution and ements of desert plants. PP- v+144- 
pls. 31. Carnegie Institution of Washington, Publication 113. 1909. 
