18 



THE UNCOILING FRONDS. 



more mature than the first ones from the prothallium 

 and will produce spores much sooner, being born 

 " grown up " as one might say. In this plant, the bul- 

 blets seem to be the chief means of continuing the 



species,while the spores 

 travel about seeking 

 new territory. Some 

 species send out stolons 

 which form new plants 

 at their tips ; others 

 produce tubers upon 

 their roots that may be- 

 come new plants ; and 

 still others root at the 

 tips of the fronds. 

 None of them, however, 

 VENATION OF A PINNA IN ASPiDiuM. are lacking in the ordi- 

 nary means of propagation. A tropical species of 

 Nephrolepis has both tubers and stolons. 



A frond that bears sporangia is called fertile to dis- 

 tinguish it from the unfruitful or sterile ones. In a large 

 number of species the two are scarcely different, except 

 for the presence of sporangia, but in others the fertile 

 are more or less changed in appearance and reduced in 

 size. 



When the blade of a frond is divided entirely to the 

 midrib, it is said to be pinnate and the divisions are 

 called pinna. When the pinnae themselves are divided ' 

 to the midrib, the frond is said to be bi-pinnate and the 

 second divisions are called pinnules or secondary pinna. 

 When frond or pinna is not completely pinnate, it is said 

 to be pinnatifid and the divisions are segments. A frond 

 may be several times pinnate or pinnatifid in which case 



