xv] 



AMPHIBIOUS PLANTS IN WATER 201 



In the case of amphibious plants, the comparison of air and 

 water shoots gives results of greater interest. Costantin 1 de- 

 scribed the anatomy of a plant of Mentha aquatica growing on 

 dry land, which happened to have the apex of one of its shoots 

 plunged into water. The young part of the stem, which had thus 

 grown in an aquatic milieu^ when compared with the older part 

 growing in air, was found to be glabrous and to have a greater 

 diameter and larger air spaces. The same increase in the air 



FIG. 132. Hydrocotyle vulgaris, L. A branch sent out into water from a plant 

 growing on the bank ; w. water level. The under surfaces of the five expanded leaves 

 were examined for stomates, which were present on all. The petiole of the air leaf 

 was more hairy than that of the succeeding leaves. July 14, 1910. (\ nat. size.) 



[A. A.] 



spaces and of the diameter of the stem, was observed in sub- 

 merged shoots of Veronica Anagallis and Nasturtium amphibium. 

 Costantin notes that, in general, when submerged plants are 

 grown in deep water, the fibrous and tracheal elements diminish 

 markedly. 



Cardamine pratensis is an example of an amphibious plant 

 which seems to pass with remarkable ease from the water to the 

 air condition. The present writer has found, on more than one 

 1 Costantin,J. (1884). 



