156 THE JOURNAL OF INDIAN BOTANY.
under the same conditions, must be due to ancestral differences, so that the same sort of idea of the facility to produce aerating tissue being the condition of a submerged life, rather than the result of it, is applicable.
Then follow chapters on the relation of the environment to the vegeta- tive and reproductive parts of water plants. It is impossible to more than mention them here, but like the rest of the book they are full of facts and suggestive ideas.
Part III is devoted to the physiology of water plants and is the shortest of the parts. Stress is laid on the fact that there is really a transpiration current, and that the problem before a submerged plant isnot how to prevent undue loss of water, but how to prevent undue accumulation. For this purpose the leaves are provided with active water-pores. The slimy covering so common in submerged parts is regarded as a by-product of the metabolism, without any particularly useful function.
Part IV, on the phylogeny and evolution of water plants is perhaps the most interesting of the whole book. The first chapter is on dispersal and geographical distribution. The special difficulties in connection with the pre- sent day occurrence of species are pointed out, and instances given which seem to support Guppy's theory of widespread primitive forms giving rise to species in different areas; and also Willis' Age and Area theory. The next is on the affinities of water plants. The idea of the Ranalian plexus being the most primitive and connected with the Monocotyledons is accepted, and it is pointed out that the aquatic families are all comparatively primitive, and that among the sympetalae are no absolutaly aquatic familes, nor even a species with hydrophilous pollination. The evidence therefore is that the aquatic families took to this life at a very early stage in the evolutionary history of angiosperms, and that possibly the more highly developed sympetalae are too far specialised for life on land to make successful colonisers of water. The Helobeae, the most important aquatic cohort, possess in the enlarged hypocotyl of the embryo, packed as it is with food, a provision which has probably been one of the chief causes of their success in aquatic life. It is this large and well differentiated cohort which has led to the erroneous conclusion that the Monocotyledons are predominatingly aquatic and to the theory of the aquatic'origin of this class. In the last chapters the bearing of the foregoing and other facts on the theory of natural selection is discussed, and evidence adduced to show that the leaves of monocotyledons are to be regarded as equivalent not to the whole leaf of the dicotyledon, but to the petiole and its sheathing base or even to the base alone, and to be in reality a pbyllode expanded into a leaf-like lamina. The last pages are devoted to a discussion on the author's principle of the Law of Loss, as explaining these and other peculiarities of aquatic plants.
The whole book is one well worth reading, indeed it might be con- sidered an indispensable part of education in advanced botany. It is well written in smooth easy flowing English, contrasting favourably in this respect with much of modern botajiical work, is very well illustrated with numerous original as well as borrowed figures, and is provided with copious bibliography.
P. F. F.
Printed and Published for the Proprietor by J. B. BUTTRICK at the Methodist Publishing House, Mount Road, Madras,
