xxvi] THE WATERS AS A REFUGE 325 



character. There is little doubt that, after they had once entered 

 upon an aquatic career, they must have evolved along lines 

 which gradually harmonised them more and more completely 

 with their surroundings, but the initial step or steps, which led 

 to the adoption of the water-habit, must have been due to an 

 innate affinity for the environment, rather than to the negative 

 quality of incapacity for success in terrestrial life; to pursue 

 our metaphor the man, who fails in the struggle for existence 

 at home, is not of the type that makes the successful colonist. 



West's 1 critical study of the vegetation of certain Scottish 

 lakes, led him to a similar conclusion, which is best expressed 

 in his own words. "It seems to me," he writes, "that aquatic 

 plants have not always had their origin from terrestrial forms 

 that had been forced into the water by more robust competitors 

 on the land, as is sometimes stated, but, more probably, because 

 certain suitable forms have exhibited a tendency, as some do even 

 now, to take on the aquatic habit, that mode of living being 

 more agreeable to their requirements, . . . never have I observed 

 the case of a plant being forced into the water by a stronger 

 competitor." 



If the preponderance of aquatic families among Monocoty- 

 ledons is neither to be explained as due to the aquatic origin 

 of the Class, nor to the part played by the waters in offering a 

 harbour of refuge to a decadent and unsuccessful race, it 

 remains to be seen whether any other interpretation can be 

 offered. In scrutinising more closely the numerical preponder- 

 ance of aquatic Monocotyledonous families, it becomes obvious 

 that this does not depend so much upon the constitution of the 

 group in general, as upon the existence of the very large and 

 highly differentiated Cohort of the Helobieae. Apart from the 

 Helobieae, there is no particular disparity between the propor- 

 tion of aquatic families in the two Classes, and, if the number 

 of species is to be taken into consideration, the theory that there 

 is a decided aquatic tendency among the Monocotyledons be- 

 comes hard to maintain. It has been pointed out 2 , for instance, 

 1 West, G. (1910). 2 Coulter, J. M. and Chamberlain, C. J. (1904). 



