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group they are large, dense, and highly colored, with very dark 

 centers. These characters at once stamp these two groups as 

 distinct from each other, though these values have been almost 

 entirely overlooked by systematists. From goldieana, celsa dif- 

 fers in its less herbaceous condition, more erect narrow habit, 

 the greater reduction of the lowermost pinnules, the more widely 

 separated smaller pinnules and less crowded apex. 



In the cristata group, which comprises D. boottii, D. Horidana, 

 D. cristata cristata and D. c. Clint oniana, the effort of the pinnae 

 to obtain the greatest amount of light is accomplished by length- 

 ening the rachis between the pinnae, thus obviating the necessity 

 of reducing the size of the lowermost pinnules. In the goldieana 

 group, however, the same effort to obtain a maximum amount of 

 light has compelled the lowermost pinnae to turn forward so as 

 to apparently escape the shading of the upper pinnae ; in doing so 

 the lowermost pinnules especially the under ones have become re- 

 duced or lost and the central ones have become longer so that 

 a reverse- condition to that of the cristata group has obtained, 

 evidently brought about by the perpetuation and evolution of a 

 simple trait or effort in accomplishing the same result in the two 

 groups by different methods. The similarity of general appear- 

 ance between D. g. celsa and D. Horidana is due to similarity of 

 ecological conditions, but otherwise they are quite distinct. 



That the flexing of a pinnae is caused by the amount of, and 

 direction of the average daily light received by it seems evident. 

 In D. cristata, for instance, the pinna simply turns from the frond 

 plane almost ninety degrees, thus bringing its upper surface ap- 

 proximately parallel with the surface of the ground, with usually 

 but slight flexing. The great distance between the pinnae, their 

 shortness and the height of the tall frond are factors which 

 render unnecessary any shortening of the basal pinnules or their 

 alternation. Thus in every specimen examined of the four forms 

 of this group the basal pinnules are the largest and are always 

 opposite, the lines of the pinnae tapering to the tip. In D. 

 goldieana the basal pinnules for most of the frond are longer than 

 the adjoining, but there is a general tendency for the middle 

 pinnules to be longest. The lowest pinnae have the basal 

 pinnules shorter than those adjoining and they are alternate, not 



