220 
Review: 
year under the title “ 0m Planterigets Livsformer.” “ It cannot,” 
says Professor Warming, be “ sufficiently insisted that the greatest 
advance, not only in biology in its wider sense, but also in oecological 
phyto-geography, will be the oecological interpretation of the various 
growth-forms: from this ultimate goal we are yet far distant.” 
Professor Warming’s system is probably the best at present 
attainable, but we should have been particularly glad of a full 
treatment of Raunkiar’s important researches, too little known in 
this country, on the kind of protection afforded to buds and shoot- 
apices by their position and otherwise. This matter is probably 
one of the most important of all ecological adaptations in plants 
subjected, as the great majority are, to recurrent periods unfavourable 
for growth. 
The treatment of ecological factors, such as light, heat, water 
and the various properties of soil, is careful and judicious throughout, 
but it demonstrates how extremely little we know about their real 
effect upon plants. In attempting to answer the question “Are the 
chemical or the physical characters of soil the more important ? ” 
—the author concludes “ that in some (few) cases, where the soil is 
specially rich in a chemical substance, it is the chemical characters 
of the soil, but in other (far more frequent) cases it is the physical 
characters that are of greatest import” (p. 70). It is no doubt true 
that where as in Denmark or the North German plain the soil is 
‘ scarcely possessed of any marked chemical characters,’ the water- 
relation becomes almost the sole determining factor, but it by no 
means follows that chemical characters may not be decisive when 
these conditions do not obtain. And there is much evidence that 
this is frequently the case. But we can say no more till a serious 
experimental attack has been made upon the question. The 
problems that the ecologist can present to the modern physiologist 
or can himself attack by the aid of modern physiological methods 
are literally innumerable, and though some are extremely complicated 
or even at present unapproachable, others (and among them this) 
seem to lie open to attack in a fairly straightforward way. 
In the new section on adaptations, matter which in the earlier 
work figured under the heads of the different types of plant- 
community is usefully brought together. Most of the section deals 
with the familiar anatomical adaptations of water plants and xero- 
phytes; there are also short sections on the amount of lignification 
found under different conditions, on stunted growth, on cushion- 
and rosette-plants. 
An excellent discussion on the determination of plant-com¬ 
munities by soil and climate introduces the author’s scheme of 
classification of the communities. 
The thirteen Classes into which Professor Warming divides 
plant communities are as follows:— 
A, Soil very wet. 
1. Hydrophytes (water-plants). 
2. Helophytes (marsh-plants). 
B. Soil physiologically dry. 
3. Oxylophytes (on acid soil). 
4. Psychrophytes (on cold soil). 
5. Halophytes (on saline soil). 
