1^4 NATURAL HISTORY BULLETIN. 



But the transition from A. kaulfussii to A. obliquum, and 

 from both of these to A. intermedium is so gradual and so 

 complete in the specimens of this collection that no clear line 

 can be drawn between them. 



In all of the characters which have heretofore been employed 

 to distinguish between A. obliquum and A. kaulfussii, there is 

 so much variation in the large series at hand that there seems 

 to be no good reason for separating them. 1 



Most of the specimens are glaucous beneath, with costa less 

 prominent, sori much interrupted, and texture less coriaceous, 

 being typical A. kaulfussii. A few specimens are wholly de- 

 void of glaucous bloom, have a distinct costa, and are coria- 

 ceous in texture, but in all these characters intermediate forms 

 connect the extremes, the amount of the glaucous bloom, the 

 prominence of the costa and the continuity of the sori being 

 especially variable characters. The pubescence of the stipe 

 is also variable, being sometimes almost wanting. 



Fig. 5, PL vi represents a pinna of a peculiar form which was 

 found near Camp Menocal. The stipe is smooth, the rachis 

 brown-hairy, the frond once-pinnate, with the pinnae acuminate, 

 and very obliquely cut at base on the lower side. It is probably 

 var. major Hook., figured on PI. lxxix A i, in Hook., Sp. 

 Fil., vol. ii. 



Both forms, kaulfussii, and typical obliquum pass gradually 

 into compound forms, the glaucous kaulfussii into typical 

 intermedium, and obliquum into the coarser triangulatum. The 

 transition of the lowest pinnae from simple to compound forms 

 is illustrated by the following figures in the order given : First 

 the simple pinnae of typical kaulfussii as represented in Fig. 5, 

 PI. v, then PI. vn, Figs. 1, 2, 3, 4, and PL vm, Figs. 1 and 2. 



By a similar series typical obliquum, Fig. 4, PL vi, passes 

 through intermediate forms of which one is represented in 

 Figs. 3, 4 and 5, PL vm (all from one frond), to a large form 



fig. 3, and pi. vn, figs. 1, 2, 3 and 4, represent forms intermediate between 

 typical A. kaulfussii and A. intermedium. 



1 Baker, Syn. Fil., p. 115, in a note under A. obliquum says that they are 

 "very doubtfully distinct." 



