II] STORAGE AND CLIMBING 35 



staple food by the Maories. Beyond a slight distension of the stock the form 

 is not altered, excepting in some few cases: for instance in Ophioglossmn 

 bulbosum and palmatum, and some other species, the stock is swollen, and 

 stored with starch, so as to resemble the corm in Angiosperms (Fig. 36). The 

 tubers borne distally on branches of the stolons of Nephrolepis provide an 

 example still more marked externally. They are oval in form, and consist 

 mainly of aqueous tissue stored with sugar. But such modifications of form 

 are rare (17). The possession of such reserve materials is often coupled with 

 a geophilous habit, but certain well-stored rhizomes are exposed above 

 ground, as in Davallia, and many species of Polypodiuni. In Pteridiiivi, 

 however, they are deeply buried, a feature which together with its unlimited 

 apical growth and frequent branching may have contributed to its world- 

 wide success. The buried storage-stock of Botiychiiim and Ophioglossum 

 may well have been a decisive condition of the survival of these ancient 

 types. 



The creeping habit is much more adaptable to the varied circumstances of 

 life than the upright with its niassive axis. Thethinner creeping stem shows 

 frequent distal branching, often with very perfect dichotomy (Fig. 32). It can 

 thus adjust itself readily to the substratum. In particular this adjustment 

 leads naturally to the scandent habit: and this finally to a full epiphytic 

 mode of life. There is little doubt that the creeping and primitive Dipteris, 

 the scandent Clieiropleuria, and the strikingly epiphytic genus Platycerium 

 are themselves illustrations showing how this last state may have been 

 acquired. Interesting parallels to this may again be found among the Aroids. 

 The climbing, and finally the epiphytic habit bring the same advantages in 

 Ferns as in Flowering Plants, and the analogies of method between the two 

 are many. The weak axis fixed to the stem of some stronger plant by 

 adventitious roots may climb to considerable heights, as is seen in Tricho- 

 inanes scandeits, and auriculatiim (Fig. 41), or venosinn (Frontispiece): in 

 Oleandra, in Stenochlaena aadeata (Fig. 42), and 5. scandens, in Polybotrya 

 osmundacea, and many others. Still greater success in climbing follows from 

 a prehensile function of the leaves, either in cooperation with a climbing 

 stem or independent of it. The latter is the case in Lygodium, where a 

 compact underground rhizome bears leaves endowed with unlimited apical 

 growth (Fig. 43). The opposite pairs of divaricating pinnae are borne upon 

 a thin wiry rachis which can twine round a support, and the plant thus 

 climbs to a very considerable height in thickets and low forest. The habit 

 is superficially like that of Medeola, and like this Flowering Plant it is 

 sometimes grown by nursery-men on strings, and used as a table-decoration. 

 Blechti^ivi {Salpichlaend)volubiIe\s also an example of the prehensile function 

 of the rachis, and is a successful climber of the Western Tropics. Other 

 Ferns have a straggling habit, chiefly due to unlimited apical growth of 



