BEAUTIFUL FERNS 
31 
almost tripinnate, and the frond has a generous breadth which 
distinguishes the variety from those already described. The 
sori are either apical, sub-terminal or medial, seated on the 
lowest anterior veins or on short veinlets derived from them, 
the position varying according to the size of the pinnules. 
In American specimens the indusium is smooth, so far as I 
have observed, and the spores are irregularly winged or 
cristate. In the plant of Europe the indusium is said to be 
usually glandular. In writing the Synopsis Filicum, Swartz 
at first united this form with A. spinulosnm, but in the 
addenda he separated the two, in which he was followed 
for a long time by most writers. I do not know that the 
first edition of the British Flora (1830) is the earliest pub- 
lication in which A. dilatatuni is made a variety of A. 
spinulosuin, but it is the earliest that I can find. 
Var. dumetoriim {A spidiuni dunietorum, Smith) is a form 
of var. dilataturn having dwarfish deltoid-ovate compactly 
bipinnate fronds and large pinnules, the inferior basal ones 
of the lowest pinnae not much elongated. It is found in 
mountainous parts of Europe ; but I have seen nothing 
exactly corresponding to it in America. It seems to be 
only var. dilafatiim dwarfed and compacted by exposure to 
the sun, and will probably be found ere long in northern 
New England or Canada. Other European sub-varieties are 
mentioned by Moore and Milde, and the student is referred 
to their writings for descriptions or figures of them. 
Var. Boottii, Gray, has been variously referred to A. 
