OUR 



THEIR ALLIES. 



poses as" \a" &bwgr!e&r plant,*- prbditemg spores instead of seeds, 

 possessing more or less woody tissue, and having its leaves 

 coiled in the bud from apex to base. After the necessary study 

 of the structure of some of our common ferns, we will be able 

 to comprehend the more technical definition found later in the 

 work. 



2. Mode of Growth. Ferns vary greatly in their method 

 of growth, yet each species has a plan which, within certain 

 limits, is fixed and definite. Some, like the common brake, 

 have their fronds rising from more or less distant portions of 

 the creeping rootstock. Others, like Asplenium trichomanes, 

 are tufted, many fronds rising irregularly in a cluster ; while still 

 others, like the ostrich-fern (Onoclea) and many of the shield- 

 ferns (Dryopteris), grow in crowns or circles, the later fronds 

 continually rising within the older ones. In the grape-ferns 

 (Botrychiuni) the rootstocks usually produce a single frond each 

 season, the bud for the succeeding year growing within the base 

 of the common stalk. 



3. In many there is a tendency to dimorphism, the fertile 

 or fruit-bearing fronds differing to a greater or less extent from 

 the sterile ones. In a few species, like the sensitive-fern and 

 the ostrich-fern (Onoclea), this is carried so far that the sterile 

 and fertile fronds bear no resemblance to each other, and in one 

 instance have been mistaken for different species, and so de- 

 scribed. Osmunda cmnamomea,. Woodwardia areolata, Pel- 

 Icea Stelleri, Cryptogramma, and Lomarza otter further exam pies 

 of this principle of growth. 



4. Variation. The same species will often present wide 

 differences in the size of the fronds. This depends to some ex- 

 tent on the character of the soil and the ordinary climatic con- 

 ditions. For example, the lady-fern (Asplentum filtx-fcemina), 

 which in ordinary locations grows from two to four feet high, 

 in mountainous regions is sometimes reduced to from three to 

 six inches, when it forms the var. exile. In like manner the 

 marginal shield-fern (Dryopterts marginalts), usually two or 

 three feet high, is reduced to five inches when growing on rocky 

 cliffs, and yet regularly produces fruit.* 



* Cf. Bulletin Torrey Botanical Club, vi. 266 (Oct. 1878). 



