BOTANICAL ECOLOGY OR TOPOGRAPHY 123 



There is, in fact, no fundamental difference between that 

 study of plant-form which we often style " adaptation " 

 and the study of the collective " physiognomy " of 

 vegetation. 



ECOLOGICAL CLASSES. An unnecessarily copious ter- 

 minology has been coined to distinguish the various 

 " ecological types " or " classes " of plants considered 

 with reference to habitat. Many of these terms have 

 been already alluded to; but it may be well to give a 

 summary of the classes here, only premising that these 

 groups neither comprehend all plants, nor are they 

 entirely mutually exclusive. 



Hydrophytes are divided into the floating Plankton 

 and Pleuston, and the rooted Benthos, Plankton 

 being microphytic, i.e. mostly Diatoms and Chloro- 

 phyceae, and Pleuston megaphytic, comprising such 

 Spermatophytes as Hydrocharis. Each subdivision 

 is again divided according to whether it is represented 

 by fresh-water or by marine plants. For example, 

 among Benthos we have the Nereid formation, of 

 Algae attached to rocks, the Enhalid formation, of 

 plants, such as Zoster a, rooted in loose soil in salt water, 

 and the Limncea formation, the equivalent of the latter 

 in fresh water including such plants as Char a and Water- 

 lilies. Hydrophytes have, as we have seen (Book II. 

 chapter x.) great mobility, especially by their methods 

 of vegetative multiplication. 



Helophytes, Hemi-hydrophytes, or Marsh-plants, include 

 two marked formations, which have been named Reed- 

 swamp and Bush-swamp. The former (Fig. 1 2) is charac- 

 terised by tall Monocotyledons, such as Phragmites, 

 Typha, and Alisma, often with creeping rhizomes, stiff 

 elastic stems, but little branched and vertical leaves. 

 The latter comprises the Alder-swamps so frequent in 

 northern latitudes, the Cypress-swamps of Taxodium in 

 the southern United States, and the thickets of Nipa 

 fruticans Thunb. in the Indo-Malayan Region. 



Hygrophytes are evergreen or sub-evergreen plants 

 growing on moist soils and in constantly moist air, such 

 as the bulk of those forming the Tropical Rain-forest. 

 Shallow rooting and drip-tips to the leaves are charac- 

 teristic features; and we may probably class here most 

 sciophytes, or shade-plants, with thin leaves, stomata 

 on both surfaces, and epidermal chlorophyll. The term 



