28 



THE HABIT AND THE HABITAT OF FERNS 



[CH. 



light which are more rehable than those of external form or general habit. 

 These lead to decisions regarding affinity which are more trustworthy because 

 they are founded on a more scientific method. 



The study of the habit of Ferns may, however, be pursued profitabl}' 

 from the point of view of the surroundings in which they grow, and of their 

 accommodation to them: in fact ecologically. It is found that their sporo- 

 phyte has been remarkably plastic under varying conditions during their 

 evolution, and that is the reason why their external habit is so unreliable 

 as a guide to affinity. The basket-form already alluded to may be regarded 



Fig. 33. Habit oi Pkyllitis {Scolopendriuin) 

 Delavayi, Franck. (After Engler and 

 Prantl.) 



Fig. 34. Habit oi Pterozonium (Gymno- 

 gramme) reniforine (Mart.) Fee. 

 (After Engler and Prantl.) 



as a central habit-type, and judging from their anatomy it appears to 

 have existed frequently among the early fossils. It follows naturally from 

 an upright position of a radially constructed axis, with slow but continuous 

 apical growth, and an acropetal succession of numerous, closely set leaves 

 of large size. A number of these developing almost simultaneously with 

 overlapping margins produce the basket-form. The short stock is suitable 

 for Ferns living as undergrowth among low vegetation, which is a very 

 frequent habitat for those of temperate climates. These considerations may 

 account for its prevalence among native Ferns. It is well represented in the 



