^ 



96 



BOTANICAL GAZE TIE 



[august 



which are conspicuous in the air leaves. The vascular system is 

 represented only by a weak development of phloem. The stem 

 of the water form is traversed by large and conspicuous air 

 chambers that connect with the leaves and the roots. The 



mechanical tissue so conspicuous in the air 

 form is absent altogether, nor can any trace 

 of conducting tissue be seen. In the axils, 

 and along the leaf margins, and terminating 

 each lobe, are gland-like structures that pos- 

 sibly function as hydathodes. 



No attempt will be made here to give any 

 account of the literature. A good deal of 

 work has been done upon other amphibious 

 plants, but the object of this paper is merely 

 to present some re- 

 sults of experiment on 

 Proserpinaca, and the 

 lite rat ure will be 

 passed over by merely 



Fig, 3. — Aerial leaf. 



mentioning a few of 



w \ 



the more conspicuous investigations upon 

 the general subject. 



Mer^ considers the aquatic form as due 

 in the main to weakened illumination and 



nutrition. Constantin^ regards it a result fj^.^L Submerged leaf, 

 of the weakening of vegetative activity. 



Schenck3 considers it largely a question of the relation to light 

 and to food absorption. Goebel, while recognizing the com- 



*Mer E., Des causes qui modifient la structure de certain plantes aquatiques 

 v^g^tant dans Teau. Bull. Soc. Bot. France 27 : 194. iSSo. 



"CONSTANTIN, J., Observations critiques sur I'epiderme des feuilles des veg^taux 

 aquatiques. Bull. Soc. Bot. France 32: 83. 1885. 



Recherches sur la structure de la tige des plantes aquatiques. Ann. Sci. Nat, 

 Bot. VI. 19: 287-331. ph. 14-17. 1884. 



Etudes sur les feuilles des plantes aquatiques. Ann. Sci. Nat. Bot. VII. 3 • 

 94-162. 1886, 



^ScHENCK, Vergleichende Anatomie der submersen Pflanzen. 1886. 



I 



