INTRODUCTION 



xvii 



as well, such as by means of bulblets, runners, or 

 by the rooting of the bent tip of the frond. ^ 



A frond bearing sporangia is known as a fertile 

 frond in contradistinction to the unfruitful or ster- 

 ile ones. In a large number of species the two 

 kinds of fronds closely resemble one another, while 

 in others they would scarcely be recognized as be- 

 longing to the same plant. 



A frond is said to be pinnate when its divisions 

 are cut entirely to the midrib (Fig. 2-A). The 

 divisions are called pinnae (singular piniia). 

 When a frond or pinna is not cut entirely to the 

 midrib it is said to be pinnatifid, and the divisions 

 are termed segments or lobes (Fig. 2-B). When 

 the pinnae are divided to their midribs the frond 

 is said to be t?vice pinnate, and the second divisions 

 are called pinnules (Fig. 2-C). 



B 



Fig. 2. 



By holding a frond to the light it may be seen 

 to be intersected by numerous veins. Wlien these 

 veins branch they are said to be forking; when 

 they terminate without connecting with one an- 

 other, they are said to be free. 



