368 MESSRS. CTEIL WEST AND H. TAKEDA ON 



Let us take another example. Isoetes ecJmiospora is always regarded as belonging to 

 " Aquatica3," auct., or to " Submersse/' Mot. et Vendr. Nevertheless, the var. B^^aunii 

 would fall into the section " Subaquaticse," Bak., and has actually been placed in the 

 " Amphibise/' Eaton (13, p. 58)*. It is surely absurd that a species and its variety 

 should belong to different sections ! 



The following examples also demonstrate the weak points in these artificial classi- 

 fications : — 



I. saccJiarata, placed by Motelay and Yendryes in their section " Palustres," is trans- 

 ferred by Baker to his " Subaquaticse." 



I. tcgulensis is also regarded by Motelay and Vendryes as belonging to section , 

 "Palustres" ; Baker, however, considers it to be one of the " Amphibiae." 



/. Tuckermanii, according to Baker, belongs to the group " Subaquaticae," but is 

 placed in " Aquaticse " by Eaton. 



I. Butleri furnishes us with a more extreme case. This species is placed in 

 '* AmphibicB " by Motelay and Yendryes and by Baker, whereas Eaton regards it as the 

 sole representative in North America of the most distinct section " Terrestres." How- 

 ever, an examination of the specimens collected by B. E. Bush at Eagle Bock, Missouri, 

 on May 22nd, 1898, has convinced us that this species cannot belong to " Terrestres," 

 A. Br. In arriving at this conclusion we were influenced by the account given by 

 Geo. D. Butler (9, p. 2j, the discoverer of the plant. This species is closely related to 

 7. melanopoda, a species belonging to " Amphibise," bat prefers less humid situations. 

 Presumably Eaton considered the last-mentioned character of sufficient importance to 

 justify its inclusion in the section '* Terrestres " ! But according to its morphological 

 and anatomical characters, this species should be placed in the section " Amphibise. 

 The definition which Eaton (13, p. 59) gives for section " Terrestres" may fit I. Butleri, 



1 



but does not agree with A. Braun*s definition of " Terrestres." 



All the above-mentioned discrepancies point to the fact that the existing classifications 

 of the genus Isoetes are both unnatural and arbitrary, being based for the most part on 

 certain very unstable morphological characters, which have been shown to vary with the 

 environmental conditions of the plant. 



Isoetes japonica furnishes us with a very clear case of this correlation of anatomical 

 characters with the habitat relations of the plant, since it may acquire the cbaracters of 

 at least three different sections of the jienus. 



It is evident that species usually included in sections "Aquaticse" or '^Submersae" 

 may so alter their characters as a direct result of a change in their environment {e.g. by 

 adopting an amphibious mode of life) as to justify their inclusion in " Subaquaticae." 

 In the same way, there can be but little doubt that any species of " Amphibiae " may live 

 entirely submerged or may even adopt a "terrestrial" habit. Possibly the species 

 belonging to " Terrestres " are only extreme forms of " Amphibiae." We are therefore 

 led to the conclusion that this artificial division of the genus Isoetes into sections can 

 serve no useful purpose. 



We may, however, distinguish two sections, comparable to the primary groups of 



• Eaton regards A. Braun as the autlior of this section, but his definition does not correspond to that of 

 " Amphibiffi," A.Br. 



?5 



