472 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
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 which 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 this 
species (shown at one-half natural size in pl. 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, 
