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 pre- 

 vent undue loss of water, but how to prevent undue accumulation. For this 

 purpose the leaves are provided with active water-pores. The slimy cover- 

 ing so common in submerged parts is regarded as a by-product of the meta- 

 bolism, 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 con- 

 clusion 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 dis- 

 cussed, 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 de- 

 voted to a discussion on the author's principle of the Law of Loss, as ex- 

 plaining 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, 



