CHAPTEK V. 



THE BIOLOGY OF A PLANT. 



THE COMMON BRAKE ,OR FERN (Pteris aquilina, Linna3Us). 



FOE the study of a representative vegetal organism some 

 plant should be chosen which may be readily procured and is 

 neither very high nor very low in the scale of organization. 

 Such a plant is a common fern. 



Ferns grow generally in damp and shady places, though they 

 are by no means confined to such localities. Some of the more 

 hardy species prefer dry rocks or even bold cliffs, in the crevices 

 of which they find support ; others live in open fields or forests, 

 and still others on sandy hillsides. In the northern United States 

 there are altogether some fifty species of wild ferns, but those 

 which are common in any particular locality are seldom more 

 than a score in number. Throughout the whole world some four 

 thousand species of ferns are known, but by far the greater num- 

 ber are found only in tropical regions, where the climate is best 

 suited to their wants. At an earlier period of the earth's history 

 ferns attained a great size, and formed a conspicuous and im- 

 portant feature of the vegetation. At present, however, they are 

 for the most part only a few feet in height. Nearly all are peren- 

 nial ; that is, they may live for an indefinite number of years. 

 Most of them have creeping or subterranean stems ; but some of 

 the tropical species have erect, aerial stems, sometimes rising to a 

 height of fifty feet or more and forming a trunk which is cy- 

 lindrical, of equal diameter throughout, and bears leaves only at 

 the summit, like a palm. 



Of all the ferns perhaps the commonest and most widely 

 distributed is the " brake" or " eagle-fern," which is known to 

 botanists as Pteris <n/i/i/!na. Linruens, or l't<'i'i<li nm aquilinum, 

 Kuhn. This plant is not only common, but of comparatively 

 simple structure ; it is of a convenient size, and has been much 



