xi] SYMPETALAE AND MONOCOTYLEDONS 151 



can produce either air leaves or water leaves with the utmost 

 facility. The floating leaves and air leaves differ in internal 

 anatomy and in the characters of the epidermis, and also show 

 obvious external differences (Figs. 99 and 100, p. 152); the 

 floating leaves are shiny, leathery and absolutely glabrous, while 

 the air leaves are wrinkled and covered with hairs 1 . The 

 lateral branches from a shoot with floating leaves, or even the 

 end of the branch itself, may rise into the air and develop the 

 characteristics of the land form 2 . 



Certain Scrophulariaceae are heterophyllous, such as Ambulia 

 (Limnophila) hottonoides and Hydrotriche hottoniaefolia. In these 

 cases the submerged leaves are finely divided. Among the 

 Pedaliaceae, Trapella* has deltoid-rotundate floating leaves and 

 linear-oblong submerged leaves, while Limnosipanea Spruceana, 

 of the Rubiaceae, also shows a distinction between water and 

 air leaves 4 . Bidens Beckii* is an example of a Composite 

 showing heterophylly. 



The heterophylly of the Alismaceae and Hydrocharitaceae 

 need not be reconsidered now, since it has been dealt with in 

 Chapters n and iv 6 . Two additional figures may, however, be 

 included here, to illustrate the effect of transferring to water a 

 small terrestrial seedling of Alisma Plantago found growing wild 

 (Fig. 101, p. 1 53). After between two and three months, it had 

 developed into the typical water plant shown in Fig. 102, p. 1 53. 



There are many other cases of heterophylly among the 

 Monocotyledons. Certain Potamogetons, e.g. P. fluitans, have 

 air leaves, floating leaves and narrow submerged leaves 7 . 

 Potamogeton natans is also a particularly good example; the 

 narrow submerged leaves may attain a length of 50 cms. in 

 running water 5 . The result of planting a land form of P. natans 

 in water has been recorded 5 . The aerial leaves soon died, and 



1 Costantin, J. (1886). 



2 Schmidt, E. M. Inaug.-Diss. Bonn, 1879, quoted by Schenck, H. 

 (1885). 3 Oliver, F. W. (1888). 



4 Hansgirg, A. (1903). 5 Goebel, K. (1891-1893). 



6 See pp. 9-14, 19-23, 51-52, 57> and Fi g s - 3-6> 9- 



7 Esenbeck, E. (1914). 



