TREE FERNS OF NORTH AMERICA—MAXON. 479 
sition contribute excellent diagnostic characters by which the species 
may be distinguished. 
LEAVES OF THE DICKSONIES. 
Of the three genera which comprise the tribe Dicksoniex, two 
(Dicksonia and Cibotium) are usually arborescent and have numerous 
large leaves borne in erect-arching crowns, as in most species of the 
Cyathez, while the third (Culcita) is very much smaller, never develops 
an upright trunk, and might readily be taken for a member of the 
family Polypodiaceew. There is evident among them not only a 
pronounced difference in size, but also in shape and cutting of the 
blades, as mentioned hereafter. They have, however, one very dis- 
tinct feature in common, namely, the development of great masses 
of delicate, limp, threadlike scales, of a type not found in many 
species of the tribe Cyathea. These are produced in great abun- 
dance upon the growing crown of the plant and extend freely along 
the stipes and rachises, from which, however, they are readily 
deciduous. They are usually yellowish or yellowish-brown and 
glistening, either straight or matted together, fragile, each com- 
posed of a single series of thin, elongate, flattish cells set on end. 
Apparently scales of no other types are produced in this tribe. The 
collection of this soft woollike substance from the crowns of several 
species of Cibotium occurring in the Hawaiian Islands was long a 
' commercial industry, the material (there called ‘‘pulu’’) being used 
mainly as a stuffing for small pillows. The wool of the Asiatic 
Cibotium Baronetz, the fabled ‘‘Seythian lamb,” and of a species of 
Culcita has been similarily used, and in a limited way also for stopping 
bleeding of wounds in surgery. 
CLASSIFICATION. 
The recognition of the Cyatheacee as a distinct family of ferns is 
based for the most part upon minute microscopical characters of the 
sporangia, the “‘spore-cases,’’ which form the sori or “fruit dots.” 
The division of the family into tribes rests in part upon similar 
characters, but also very largely upon more apparent differences in 
the form of the indusia, special outer structures which more or less 
completely inclose and protect the sporangia during their period of 
development. As already stated the North American species are 
associated in two tribes, the Cyathee and the Dicksoniex, whose 
main diagnostic characters may be readily recognized. 
The tribe Cyathee is distinguished by having the sori borne 
directly upon the ultimate veins of the segment and never at the ends 
of the veins, which extend nearly to the margin. The sorus may in 
different genera be either naked (without a special protective outer 
structure) or either partially or wholly surrounded by such an organ, 
