n] 



THE GEOPHILOUS HABIT 



31 



of 60 or even of 70 feet in Dicksonia and in the genera closely allied with 

 Cyathea. In all of these the sporeling is prone, and the apex assumes the 

 upward position as it develops. This being so it cannot be assumed that 

 the dendroid habit is in itself a sign of affinity of those Ferns, inter se, much 

 less with the more distant Marattiaceae. It may well have been achieved 

 independently by each type that shows it. The result is, however, the most 

 striking of all the developments of Ferns. Tree Ferns flourish best under a 

 high forest-canopy, though individuals often project upwards through lo\\- 

 undergrowth, where the climate is sufficiently moist. 



A curious modification of the upright habit is seen in the geophilous 

 Ophioglossaceae, which are by its means able to adjust their mode of life 



B 



Fig. 37. Helminthostachys zeylanica. A = young plant still attached to prothallus, showing 

 vertical position of axis. ^ = adult plant with rhizome horizontal. A after Lang, j5 after 

 Farmer and Freeman. .^'=stipular flap; Z = leaf; /*= petiole; Z5'= leaf-scar ; R = xqo^. 



to the requirements of marked seasonal change. The axis in Botrychium 

 and Ophioglossum is short, upright, and deeply buried in the soil, and it is 

 largely composed of storage-parenchyma. From it, in most of the large- 

 leaved species, one leaf is expanded annually above ground, and it function- 

 ates for both nutrition and propagation. In some of the smaller species, 

 such as O. liisitanicinn and O. bidbosiim, two or three, or as many as six 

 leaves may be expanded in each year. At the end of the season the leaves 

 rot away, and the product of their activity is stored in the stock for the 

 succeeding season (Fig. 36). This monophyllous habit is suitable for meeting 

 seasonal needs. During a period of drought or low temperature the plant 

 perennates underground, but its expanded leaf or leaves carry on nutrition 



