468 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



tant role of conserving moisture by preventing radiation and the 

 consequent drying out of the forest floor. 



Perhaps a majority of tree ferns, however, occur as an integral 

 part of the predominant forest growth, their crowns often reaching 

 nearly or quite to the level of the tree tops, or in not a few species 

 even exceeding it; as, for instance, Oyathea pubescens, one of the tallest 

 Jamaican species, which attains a height of 40 feet or more upon 

 the heavily forested higher ridges of the Blue Mountains and easily 

 thrusts its crown above the surrounding deciduous forest. There 

 are also certain species, like Alsophila parvula, Oyathea furfuracea, and 

 C. insignis, which in Jamaica grow indifferently in open and shaded 

 situations, though their occurrence in the open may have followed 

 naturally from the partial and piecemeal clearing of the land, the 

 small cleared patches remaining under cultivation only a year or 

 two before rapidly growing up to bush. It is noticeable that those 

 individuals growing in the open often acquire a condensed or stunted 

 form, as described later. 



At least one species, Oyathea arborea, flourishes in open situations, 

 commonly in very large colonies. Jenman has described it in 

 Jamaica as u gregarious, often covering acres on fully exposed slopes, 

 everywhere shunning shade." Perhaps on the latter account, and 

 also because of its ubiquity, it is found more commonly than any 

 other about dwellings and plantations, its huge, lacelike fronds 

 lending an unusual decorative charm to scenes already novel and 

 interesting to northern eyes. The formation of groves by this 

 species in relatively dryish, open situations is almost unique for the 

 family, although a few (e. g., Alsophila armata) are more or less gre- 

 garious in partial shade, and many others of our American species 

 are found in colonies in the deep, wet forest. In New Zealand the 

 social tendency has even resulted in the formation of large groves 

 under intensely humid conditions. One of these, which Colenso 

 came upon in the forest called "Seventy-mile Bush," in North 

 Island, is described by him as follows: 



On a flat in the heart of the forest, in a deep hollow lying between steep hills, the 

 bottom of which for want of drainage was very wet and uneven and contained much 

 vegetable mud and water even in the dryest summer season, I found a large and con- 

 tinuous grove or thicket of very tall tree ferns, chiefly Dichsonia squarrosa and D. 

 fibrosa, with a few of Oyathea dealbata intermixed, with but few forest trees and shrubs 

 growing scattered among them. I suppose they occupied about 3 roods of ground, 

 and I estimated their number to be 800 to 1,000. They were all lofty, from 25 to 35 

 feet high, and in many places growing so close together that it was impossible to force 

 one's way through them. 



Concerning tree-fern formations of this sort in both New Zealand 

 and Australia, Christ has pointed out that they rarely consist of a 

 single species, but are as a rule mixed associations of two or more 



