CH. xxvi] AQUATIC GEOPHYTES 323 



aquatic habit and endogenous structures." Further, Henslow 

 points out that Monocotyledons and aquatic Dicotyledons have 

 many characters in common, and he explains these resem- 

 blances, and the numerical preponderance of aquatic Mono- 

 cotyledons, on the theory that Monocotyledons have arisen 

 from a Dicotyledonous stock through ''self-adaptation to an 

 aquatic habit." 



Henslow's theory has been criticised in some detail by Miss 

 Sargant^, who has shown that a large proportion of the charac- 

 teristic features of Monocotyledons can be more readily inter- 

 preted on the supposition that the group was evolved through 

 adaptation to a geophilous habit, than on the view that it was 

 originally aquatic. The resemblances between aquatic plants and 

 Monocotyledons are, on her view, largely due to the fact that 

 both have suffered some reduction and degradation of structure, 

 not necessarily arising from the same cause. It is true that the 

 type of plant reconstructed by Miss Sargant, as representing the 

 ancestral Monocotyledonous stock, would be, as she has pointed 

 out, well adapted for subsequent aquatic life. Many aquatic 

 Dicotyledons are formed more or less upon the geophilous 

 plan, e.g. Nymphaea (Fig. 10, p. 25), Castalia (Fig. 11, p. 26), 

 himnanthemum (Fig. 22, p. 41), hittorella (Fig. 142, p. 218). 

 It is worthy of note that, in an instance in which an aquatic 

 flora that of the Jura lakes was analysed from this point of 

 view^, of the forty aquatic Phanerogams and Vascular Crypto- 

 gams recorded, thirty-one proved to have rhizomes. 



The main lacuna in Henslow's theory appears to be that it 

 treats the reduction of the cotyledons, from two to one, merely 

 as a symptom of the general degeneracy of Monocotyledons, 

 whereas Miss Sargant's theory of the geophilous origin of 

 Monocotyledons offers a specific and convincing explanation 

 of this peculiarity. 



If Henslow's theory be not accepted, the onus rests upon his 

 opponents of explaining the existence of so large a proportion 

 of aquatic families within the Monocotyledons. Miss Sargant 

 1 Sargant, E. (1908). 2 Magnin, A. (1893). 



21- 



