TREE FERNS OF NORTH AMERICA MAXON. 477 



the blades, but also upon the leaf tissue. In these characters the 

 members of the tribe Cyatheae show almost infinite diversity. 



In many species of Cyathea and Alsophila, and less commonly of 

 Hemitelia, the trunks are more or less completely covered with 

 spines, a fact which no one who has reached out hastily and grasped 

 one in a futile effort to stay his rapid descent down some steep, 

 slippery, forest-clad slope, is likely to deny. As a rule, however, the 

 trunks are spiny simply from the partial persistence of the broken 

 stipe bases, which indisputably are spiny. Two stipe bases thus 

 armed are shown in plate 5; of these figure B represents Cyathea 

 onusta, and figure C, C. aureonitens, both species of Costa Rica and 

 western Panama. The last mentioned is one of those which really 

 produce spines upon the trunk also, and these, like those of the stipe, 

 of needlelike sharpness. In certain species the spines are long, 

 straight, columnar, and blunt; in others low and broadly conical, with 

 a hooked point; in still others slender and sharp, but very short and 

 closely set. The conical, more or less curved form is the commonest 

 one among North American species. In Cyathea arborea (pi. 5, fig. A) 

 they are evident only as low tubercles, and in not a few others they 

 are altogether lacking. They are usually produced only upon the un- 

 derside of the stipe, in some species extending in lessened size and 

 number along the rachis well toward the apex of the blade, as may be 

 seen in Alsophila aspera (pi. 7). In color spines range from yellow 

 to brown, purple and black, usually taking the color of the stipe or 

 presenting a darker and highly polished surface. They have been 

 said to be poisonous, though the truth of this is certainly open to doubt. 



The stipe is otherwise furnished with large protective scales which, 

 however varied in character, are as distinctive for each species as are 

 the spines of each. These scales closely invest the apex of the crown 

 in a thick, upright, brushlike mass. The young fronds, like those of 

 all ferns, as they unroll from the bud carry with them their scaly 

 covering. (Plate 6 represents at natural size a young expanding 

 frond of Cyathea arborea.) The great majority of the large scales 

 which develop upon the frond as it increases in size are, however, 

 readily deciduous ; and as a rule only those of the lower stipe, and more 

 especially those which are seated in the deep axils of the stipe bases, 

 persist until the frond attains maturity. The latter are precisely 

 like those of the crown, of which, in fact, they are really an integral 

 part. Thus constituted, the cap or head of the crown consists ordi- 

 narily of scales so closely packed together that they serve as a very 

 effective, impervious, protective covering, not only against excessive 

 moisture and consequent infection from without, but also as a safe- 

 guard, enabling the plant to maintain without interruption its vital 

 activities at the one essential point, the apex, despite unusual ex- 

 tremes of dryness, heat, and cold. The utility of the chaffy cap is 



