BOTANICAL GAZETTE. 252 



nolia. Indeed, any true sunken gland my be regarded as an internal 

 epidermal organ. 



Plants which do not live either entirely in the water or entirely 

 out of it may naturally be expected to occupy, so far as their oganiza- 

 tion is concerned, a position intermediate between submerged plants 

 and aerial plants. Such is the case with the Nympha?acea;. While 

 not relinquishing their dependence upon, and their connection with, 

 the external atmosphere, they nevertheless provide against partial sub- 

 mergence, by an increase of their capacity for internal interchange of 

 the gases necessary for their life and growth. In other words the 

 amount of external surface exposed to the atmosphere being largely 

 curtailed, by reason of their jiariial submergence, this loss is compen- 

 sated for by a great increase in the amount of internal surface exposed 

 to the air and gases contained in the intercellular spaces. By this en- 

 largement of the intercellular spaces the inside of the plant becomes 

 {if I may be allowed the paradox) to some extent, for physiological 

 purposes, another outside ; and the practical effect is the same as if 

 there were less intercellular space, and more surface exposed to the 

 outer atmosphere. To the same extent as the inside becomes practi- 

 cally a part of the outside, by reason of its exposure to surrounding 

 air and gases, that part of the outside which is submerged becomes 

 practically part of the inside, by reason of its exposure to the sur- 

 rounding fluid. 



In plants existing under such peculiar circumstances, we need 

 not be surprised to find organs and tissues, which in strictly terrestrial 

 ])lants are external, becoming internal. And so there is no a priori 

 reason against the existence of internal hairs, or even of a whole in- 

 ternal epidermal system, in the Nymphix^acege. But we have no war- 

 rant for looking for internal hairs in all partially submerged, or 

 wholly a(pialic, plants any more than we have for expecting to find 

 external nairs upon all terrestrial or aerial plants. As a matter of 

 fact hairs do not exist u])on many land plants which seem to grow 

 under the same circumstances and surroundings as others 

 upon which hairs arc found ; and so, while Nymphiva and Nu- 

 phar are internally pubescent, Nclulmtm and Brascnia are internally 

 glabrous. It is no easier to account for this difference in land-])lants 

 than it is in water-plants ; but in both cases it is doubtless caused by 

 some fundamental, physiological difference at present unknown. 



That the great enlargement of the intercellular spaces in sub- 

 merged, or partly submerged plants is for the purpose of facilitating 

 the internal interchange of gases which, in plants, growing upon 

 the land, would take jjlace externally, is no new theory of my own. 

 Sachs, in his "Botanical Text-Book," says: 



"A submerged water-plant, for exam])ie, which contains chloro- 

 phyll, absorbs carl)on dioxide from without, under the influence of 

 sunlight; and at least a jiortion of the disengaged oxygen collects in 

 the cavities. When it becomes dark this ]irocess ceases ; the collect- 

 ed oxygen is now absorbed by the fluids of the tissues, and gradually 

 transformed into carbon dioxide, which can again diffuse back into 



