4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



A reasonable explanation of the remarkable leaf form developed 

 by many individual fronds is, I believe, found in the following- 

 hypothesis, which has been substantiated by a careful examination 

 of the series of specimens. It is that, notwithstanding the inde- 

 terminate g-rowth of the lamina and of the pinnae at their apices, 

 the fronds would, if fully protected from injury by natural causes 

 (such as injury by wind or by the falling of water-filled parasites 

 from the heavily laden branches above), develop in a nearly sym- 

 metrical form. (See Plate i, in which the frond had apparently 

 attained a fair size before the apical portion was lost. There is no 

 abortive tip : the whole apical portion has been broken ofif.) Plate 

 2 would appear to controvert this supposition somewhat ; but an 

 examination of the specimen itself shows the apex of this frond to 

 be dead and discolored, and the other live or six fronds to have 

 been broken ofT short and to have "forced " the activities of the 

 entire plant to seek an outlet through a single channel, namely, the 

 further development of the pinnae of the one remaining frond, each 

 (if uninjured) with its nearly dormant or slowly unrolling minute 

 terminal bud. The alternative would have been the development 

 or pushing out of new fronds, a feature which is, possibly, seasonal. 



Further evidence is oiTered by a great number of mutilated 

 fronds, and in particular (among the mounted specimens) by one 

 not here figured (U. S. Nat. Herbarium, no. 676090) which has the 

 stipe short and stout, the rachis 7 cm. long, the lamina there 

 broken ofif sharply by natural injury and wanting, the pinnae miss- 

 ing on one side of the basal remnant, and those on the other side 

 several times dichotomous and produced to a length of 18 cm. A 

 frond of another plant has several pinnae similarly developed to a 

 length of from 18 to 24 cm. 



Instances of indeterminate growth in Polyopodium are, I think, 

 not very common, but the following readily occur: (i) That of P. 

 jamesonioides Fee', a species described from Colombia (6V/^//w 399), 

 recently collected by me on Chiriqui Volcano at an altitude of 

 about 3,000 meters (no. 5340), in which the slender simply pinnate 

 fronds are obviously of indefinite evolution, the apex being inva- 

 riably terminated by a crosier-like nascent bud: (2) that of P. 

 heieromorplnim Hook, and Grev., which with its dichotomous 

 fronds is well known in several forms; (3) and that of the West 

 Indian P. airvatum Sw. (of which P. inaequale Fee^ is an exact 



1 F^e, 7iTie M^m. Foug. 59. pi. 21. f. 4. 1857. 

 -Fee, iinie M^m. Foug. 47. pL 12. f. .?. 1866. 



