1897.) Vegetable Physiology. 437 
But plants must adapt themselves not only to the physical conditions 
mentioned, but also to animals and to other plants. Man is far from an 
insignificant factor. The interdependence of plants and animals, such 
as flowers and pollinating insects, plants and ants, etc., though not 
discussed at length, plays a more or less important part in the battle. 
The greatest struggle, however, is that which takes place between the 
plants themselves. A more or less stable equilibrium has been estab- 
lished in several ways. Parasitism, helotism (applied by the author to 
the relation of organisms in the lichen thallus), mutualism (root tuber- 
cles, etc.), epiphytes, with all their curious adaptations, saprophytes, 
lianas, are carefully considered. Over a given area where the various 
factors are comparatively constant, certain species are found which have 
adapted themselves to these conditions and to each other. These 
together make the plant community and present to the eye a certain 
physiognomy. Two plant communities living under similar conditions 
may present similar physiognomies, but may consist of widely different 
series of species. With the exception of subglacial and desert regions 
there is a conflict among individuals, those inherently less hardy and | 
those accidentally unfavorably placed being first to succumb. 
Hence, we have a kind of association known as commensalism. This 
term is sometimes used in the sense of mutualism (symbiosis) ; but, as 
used by the author, it means rather an established equilibrium between 
individuals struggling for the same food. It is to be noted that the 
strife between individuals of the same species is much greater than that 
between individuals of different species, since, for example, they may 
use different materials in the soil. 
The first 120 pages of the work is taken up with pakaa dis- 
cussions, as briefly outlined. The author gives a classification of the 
various plant communities. They are grouped in four classes, depend- 
ing upon the relations of these to water. “ The regulation of transpira- 
tion of plants appears to be the factor which influences most profoundly 
the forms of plants, and which imprints upon them most markedly their 
external characters. If the evaporation is greater than the water supply, 
the plant wilts, and this influences the most important life processes, 
even if it does not go so far that death results.” 
The classes are as follows: 
“I. HYDROPHYTE-VEGETATION. —This is an extreme vegetation 
whose plants are either wholly, or, for the most part, surrounded by 
water, or grow in soil well filled with water (the per cent. of water 
amounts to probably more than 80). 
