i88i:] 



MICEOSCOPICAL JOTJKNAL. 



131 



That structures physiologically re- 

 ferable to the epidermal system 

 should be found growing in the midst 

 of the parenchymal system, is not alto- 

 gether ajiomalous, for sections of the 

 leaf and petal oi Magnolia grandiflora 

 reveal an abundance of thickened, 

 irregular, unicellular structures scat- 

 tered through the parenchyma, which, 

 both in their appearance and in their 

 mode of distribution, at once suggest 

 some sort of similarity to the inter- 

 nal hairs of Nymphcea and Nuphar; 

 but which, in my judgement, are parts 

 of the glandular system of the Mag- 

 nolia. Indeed, any true sunken gland 

 may be regarded as an internal epi- 

 dermal organ. 



Plants which do not live either en- 

 tirely in the water or entirely out of it 

 may naturally be expected to occupy, 

 so far as their organization is con- 

 cerned, a position intermediate be- 

 tween submerged plants and aerial 

 plants. Such is the case with the 

 Nymphaeaceae. While not relinquish- 

 ing their dependence upon, and their 

 connection with, the external atmos- 

 phere, they nevertheless provide 

 against partial submergence, 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 ex- 

 posed to the atmosphere being largely 

 curtailed, by reason of their partial 

 submergence, this loss is compensat- 

 ed 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 sur- 

 face exposed to the outer atmos- 

 phere. To the same extent as the 

 inside becomes practically a part of 

 the outside, by reason of its exposure 

 to surrounding air and gases, that 

 part of the outside which is sub- 



merged becomes practically part of 

 the inside, by reason of its exposure 

 to the surrounding fluid. 



In plants existing under such pecu- 

 liar circumstances, we need not be sur- 

 prised to find organs and tissues 

 which, in strictly terrestrial plants, are 

 external, becoming internal. And so 

 there is no a priori reason against the 

 existence of internal hairs, or even of a 

 whole internal epidermal system, in the 

 Nymphasacese. But we have no war- 

 rant for looking for internal hairs in 

 all partially submerged, or wholly 

 aquatic, plants, any more than we 

 have for expecting to find external 

 hairs upon all terrestrial or aerial 

 plants. As a matter of fact, hairs do 

 not exist upon many land-plants 

 which seem to grow under the same 

 circumstances and surroundings as 

 others, upon which hairs are found ; 

 and so, while Nymphcea and Nuphar 

 are internally pubescent, Nelubimn 

 and Bracenia are internally glabrous. 

 It is no easier to account for this dif- 

 ference in land-plants than it is in 

 water-plants ; but in both cases it is 

 doubtless caused by some fundamen- 

 tal, physiological difference at present 

 unknown. 



That the great enlargement of the 

 intercellular spaces in submerged, or 

 partly submerged, plants, is for 

 the purpose of facilitating the inter- 

 nal interchange of gases which, in 

 plants growing upon the land, would 

 take place externally, is no new 

 theory of my own. Sachs, in his 

 " Botanical Text-Book," says : — 



" A submerged water-plant, for ex- 

 ample, which contains chlorophyll, ab- 

 sorbs carbon dioxide from without, 

 under the influence of sunlight ; and 

 at least a portion of the disengaged 

 oxygen collects in the cavities. When 

 it becomes dark this process ceases ; 

 the collected oxygen is now absorbed 

 by the fluids of the tissue, and gradu- 

 ally transformed into carbon dioxide, 

 which can again diffuse back into the 

 cavities, but partially also through 

 the layers of tissue into the surround- 

 water." 



