CH. XIV] THE TROPOPHYTES 567 



^DELIQUESCENT TREES ; the greatest of all vegetation, a 

 dome of foliage supported on branches radiating from a 

 single trunk (page 181), which is wide rooted in aerated soil; 

 typified by the greater trees of the tropical forests, and 

 by the summer condition of our own deciduous forest 

 trees. Maples^ Oaks, Elms, Beeches, etc. (Fig. 123). J^OLUM- 

 NAR TREES^ upright, unbranched, columnar trunk, with a 

 reat crown of pinnately compound fronds usually lifted 

 above all surrounding vegetation ; typified by the Palms 

 (Fig. 30) ; in the Tree Ferns (Fig. 31), and the greaterCycacls 

 (page 517) the form survives, though now as undergrowth. 

 _DWARF COLUMNAR TREES^; like the preceding but short 

 stemmed with fan-shaped leaves ; typified by Dwarf Palms 

 (Figs. 30, 34, 377). JJIANT HERBS ; of rapid soft growth to 

 great size in sheltered situations ; typified by the Banana 

 (Figs. 28-29) and many great Aroids. GIANT G:RASSES; 

 typified by Bamboo (Fig. 374). STILT SHRUBS; the shoot 

 raised above ground upon prop or stilt roots, typified by 

 Pandanus (Fig. 177). 



B. THE ALTERNATING HUMID-DRY HABITATS, AND THE 

 VEGETATION FORMS CALLED TROPOPHYTES. _^ 



In some habitats, otherwise optimum, water is scant or 

 unavailable during much of the year, and thus the plants, 

 mesophytic for parf. of thft tin^e, are perforce xerophvtic for 

 the remainder. This condition obtains in some dry parts 

 of the earth, but is most familiar in our own temperate cli- 

 mate, where the plants find plenty of water in summer, but 

 not in winter, because roots absorb badly from cold soils, 

 and not at all from those that are frozen. Thus our winter 

 soils are physiologically even though not physically dry, 

 and our plants in winter are exposed to desert conditions. 

 Correspondingly, the typical temperate vegetation, while 

 spreading ample thin foliage in summer, largely sheds the 

 leaves, and protects itself against desiccation, for the winter. 

 Thus are produced vegetation forms which are alternately 



