— U9 — 



likely to scatter them into such places as the plant nor- 

 mally occupies, which are in the crowns of lofty trees. 



It is probable that a considerable majority of all ferns 

 have the fructification developed toward the apex rather 

 than toward the base of the frond, obviously favoring 

 the greater dryness of the fertile region. There are all 

 grades of specialization in this respect from that in which 

 the preference of the sori for the distal end is doubtful 

 or not, emphasized as in the case of many species of 

 Nephr odium, Poly podium, etc. The adequate drying of 

 the mature reproductive structures without jeopardy to 

 the proper performance of the vegetative functions is 

 accomplished in many ferns by the specialization of en- 

 tire fronds for one or the other end. In many ferns 

 there is little or no specialization other than a difference 

 in the length of the stipes, those of the fertile frond being 

 the longer. In Pteris there is a difference in the mar- 

 gin, and in P, cusi folia the fertile frond is less compound 

 than the sterile. The fertile fronds of Poly podium sinu- 

 osum yield to drought and fall off before the sterile. 



There still remain a few ferns in which the differen- 

 tiation has gone so far that the assimilating but not the 

 spore-bearing surface of the frond has been practically 

 obliterated. These are Leptochihis and Cheiropleuria, 

 still with some expansion of green lamina, the nether 

 surface of which is completely covered, when mature, 

 with sporangia; Blcchnum egregium, the fertile pinnae 

 of which are expanded at the base only, and Psomiocarpa, 

 Stenosemia, Stenochlccua and Lomagramma, whose fer- 

 tile fronds are almost completely without assimilating 

 tissue. The two scandent genera have the pinnae articu- 

 lated to the rachis and the pinnae of the fertile fronds of 

 both are much more caducous than those of the sterile. 

 This, with the further fact that only plants of a very 

 considerable age are fertile, makes fertile fronds of both 

 hard to find. The fertile frond of Blechnum egregium 

 as well seems to be both rare and transitory, and on all 

 these ferns they are to be found only in season. 



