WATER PLANTS 297 



there is to do when one knows the names of all the plants available. 

 Since ex})ansive accounts and an exhaustive nomenclature of critical 

 sub-species have little interest for students brought up to contemplate 

 the mutants of QSnofliera, and the facile assumption of hybrids 

 which rest on no experimental evidence does not excite those who are 

 taught that such forms will Mendelize out. Floras devoting space 

 to such conventions are obsolete before they are issued, and a working 

 account of the biology and ecology of the living plant is a desideratum 

 far bevond even the authentic herbarium-specimens of an Exchange 

 Club. ' 



Starting from tlu; standpoint that the special plants of fresh-water 

 streams and ponds are particularly available in the Cambridge district, 

 Mrs. Arber has attempted a review of essentially aquatic types of 

 lowering plant which may serve as a model for the examination and 

 illustration of other biological groujjs of the British iiora. As the 

 author points out, no indigenous Angiosperm vegetation is so markedly 

 aberrant from what passes as normal habit, as the regressiA^e flower- 

 ing plants of ponds and even of the sea ; while in these daj's of rapid 

 enclosure of woods and common land, and the march of cultivation 

 implied by improved agriculture, such aquatic stations alone tend to 

 retain their original inhabitants comparatively unaffected, as well as 

 ready of access to the casual botanist. 



The text includes a very full description of the organization and 

 habit of such plants as Sagittaria, JSfijniplicea, Ili/drocharis, Potamo- 

 getons, Utricularias, and Water-Ranunculi, with chapters on their 

 special anatoni}', their flowers and fruits, physiological processes and 

 ecology, taking the last term in its widest significance. In order to 

 give a wdder outlook, more striking exotic examples are touched on, 

 as Podostemacete and tlie marine Halopltiht and Posidoiiia. More 

 speculative sections inti-oduce references to the 'Law of Age and 

 Area,' and the ' Law of Loss ' ; thougli, as in the case of the ' Law of 

 the Survivor of the Fittest,' it is doubtful wdiether one gains more than 

 a definition of the terms employed. It is refreshing in such a volume 

 to find s^^stematy kept well in the background ; for example, Limn- 

 anthenunn is bracketed with Nymplicea. The text may run thin in 

 places, as in the account of the floral mechanisms of the Nymphseacea?, 

 and in details of fruit and seed-formation, and there is an excusable 

 bias for recording ancient history ; but the volume covers a wide 

 range of introductory work, and as such will be welcomed by the 

 student of the British Flora as a standard compendium of information 

 on aquatics. 



The method of interpretation reflects the attitude in which 

 students of the last generation have been taught to consider the 

 mechanism of derivation and adaptation, however much one may 

 wonder sometimes if the prol^lem is stated the right way ; since the 

 ' Law of Loss ' is but a corollary of the basis on which it has been 

 possible to build the science of comparative morpholog}^. A deep 

 respect for authority, again, which is less required when one has the 

 living plant to deal with, finds expression in the extension of the 

 usual list of references to 65 pages, thus swollen ly the addition of 

 brief notes on the content and scope of the memoirs — a somewhat 

 Journal of Botany. — A^ol. 58. [December. 19-!0.] 2 a 



