472 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19IL 



Other species show this trait to a lesser extent; and while a few 

 seem to maintain always their full complement of leaves, it is doubt- 

 less true that most tree ferns bear their greatest number of leaves 

 during the moister, vegetative season, and a smaller number while 

 resting between active growing periods. An accentuation of this 

 tendency might easily lead, and doubtless has led, to the complete 

 seasonal shedding of fronds in the several species mentioned. This 

 conclusion is strengthened by our knowledge of the development 

 of the habit by different species upon widely separated areas, and is 

 not invalidated by the fact that these are associated with other 

 species, apparently under identical conditions of environment, in 

 which this trait is not in evidence. 



VARIABILITY IN RATE OF GROWTH AGE. 



Of the species which under humid forest conditions ordinarily 

 produce lofty trunks, certain individuals growing in more open 

 situations will often be found much reduced in stature. One of 

 the best illustrations of this to come under my observation is that of 

 Cyathea furfuracea, a species winch is very common in the forests of 

 the Blue Mountains of Jamaica, occupying a broad belt between 

 4,000 and 6,000 feet, and occasionally attaining a height of 40 feet or 

 more. Dwarfed specimens upon partially cleared slopes, although 

 often only 3 or 4 feet high, still retain their erect arborescent character, 

 however slow the development of the trunk may be, and differ from 

 the more luxuriant individuals growing in moist shade mainly in 

 their smaller fronds and more closely set leaf scars, the last a definite 

 mark of the plants of slow growth. The same species as I met 

 with it upon the shrubby open slopes of the Gran Piedra in eastern 

 Cuba, at 4,000 feet elevation, is even more reduced, its trunk measur- 

 ing from 1 to 2 inches in thickness, its fronds one-third to one-half 

 their usual size. This phenomenon of reduction in size as a result of 

 excessive insolation, and consequent drying out of the substratum, 

 is commonly observed in most groups of ferns whenever plants 

 normally shade inhabiting are thrust into^the open. Johow has 

 stated that the great tree ferns of Juan Fernandez develop as well in 

 the sun as in shade; but such a condition, we must believe, is excep- 

 tional. 



Another excellent example of the variability in rate of growth is 

 found in Cyathea arborea, as evidenced by two trunks, both of tins 

 species (shown at one-half natural size in pi. 3), which I collected 

 upon the southern slope of the Sierra Maestra of eastern Cuba in 

 March, 1907. The plants of which figure A represents a typical 

 trunk section were about 35 feet high and slender, with a compact 

 crown of medium-sized leaves spreading widely from the trunk, 



