202 



LAND AND WATER FORMS 



[CH. 



occasion, that an entirely submerged plant, when placed in soil 

 under ordinary aerial conditions, rapidly developed into a 

 typical land plant. Schenck 1 has described the comparative 

 anatomy of submerged and aerial plants of this species. The 

 anatomy of the submerged stem showed several points of 

 interest. The intercellular spaces and the diameter of the cortex 

 were increased; the vascular cylinder had approached nearer the 

 centre of the stem; all mechanical elements were absent, and 

 the xylem was reduced (Fig. 133, cf. A and #). In the case of 



C D 



FIG. 133. Cardamine pratensts, L. A, T.S. stem of land form. B, T.S. submerged 



stem; rp = cortex, m = pith, mr = mechanical ring. C, T.S. leaf of land form. D, 



T.S submerged leaf. [Schenck, H. (1884).] 



the leaves, those that were submerged had developed no palisade 

 tissue (Fig. 133, cf. Cand D). 



Such anatomical work as that briefly outlined above, leads 

 to the general conclusion that when amphibious plants are grown 

 in water they readily acquire the characters which we regard 

 as typical of aquatic plants, but that, when terrestrial plants are 

 grown under similar conditions, the changes which occur, 

 though trending in the same direction, are very much less 

 marked. There seem to be two possible, alternative explanations 

 of this difference of behaviour. On the one hand it may be that 

 1 Schenck, H. (1884). 



