480 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
theindusium. If an indusium of any sort be present, it isnever formed 
of any portion of the leaf margin, but is developed separately, being 
attached at the base of the receptacle—the raised conical, globose, or 
club-shaped structure upon which the sporangia are borne. 
The tribe Dicksoniex, on the other hand, has all the sori produced 
upon the ends of the veins; that is, they are truly terminal and 
marginal. In this tribe the sorus is invariably provided with a 
bilobed or bivalvate irdusium of a wholly different character from 
that of the Cyathee, since it is formed in part by the more or less 
modified and concave margin of small lobes of the leaf segment, 
these facing inward. A similarly fashioned concave inner lip, facing 
outward, arises from the base of the receptacle. Thus the two lips 
together constitute the ‘double”’ (i. e., bilobed or bivalvate) indusium 
mentioned above, within which the sporangia are contained. At 
maturity the lips are thrust widely apart by the expanding sporangia. 
These are the more obvious technical characters by which the two 
tribes may be distinguished. Without entering very far into the 
subject it may be well to indicate briefly the grounds for recognizing 
the several genera constituting these. Recourse will be had to 
illustrations showing the parts upon a greatly enlarged scale, which 
will serve far better than description alone to indicate the position 
of the sori and to emphasize distinctions in form and structure of 
the indusia. 
THE TRIBE CYATHEZ. 
The tribe Cyathez was divided long ago into three genera, Cyathea, 
Alsophila, and Hemitelia, mainly upon characters of the indusium; 
and this conception has prevailed generally down to the present time. 
It happens, however, that within the limits of this tribe there is found 
nearly every intermediate stage between a complete hollow sphere 
wholly inclosing the sporangia and the absence of any indusium 
whatever. Because of this, the justification for laying great weight, 
as a basis of generic classification, upon structures of such an ephem- 
eral and variable nature has been seriously challenged by nearly 
every recent writer upon ferns; and also because in many other 
groups of ferns the indusia are now looked upon as really of such 
secondary importance as often to preclude their use for more than 
minor taxonomic distinctions, though they may be very serviceable 
in distinguishing species or for associating them in minor groups 
below the rank ofagenus. The proposition again put forward, of late, 
to merge Cyathea, Alsophila, and Hemitelia under a single generic 
name (Cyathea) is thus not without merit. Yet, considering our 
present incomplete knowledge and the extent of data still to be 
derived frorh a thorough study of the group as a whole, it seems 
desirable to hold to the established classification until a better one 
