TREE FERNS OF NORTH AMERICA—MAXON. 473 
their attachment being nearly at right angles. The plants of which 
figure B represents a trunk section were rather shorter and more 
robust, with an immense crown of larger fronds rising from the 
trunk like a huge funnel, their leaf stalks being suberect and in 
attachment extending from the apex a distance of several inches 
down the trunk. At the time these plants were collected they were 
believed to represent two very different species. Nevertheless, 
upon careful study subsequently it was found that they possessed no 
technical differences whatever by which they might be recognized 
as distinct, aside from the difference in shape and size of leaf scars, 
even the scales of the trunk and leaf bases being exactly alike except 
as to size; and the conclusion was forced that these were forms assumed 
by asingle species, the differences noted in the trunks being dependent 
upon the age and vegetative vigor of the plants. This conclusion was 
substantiated later by an examination of several living West Indian 
plants of this species in the conservatories of the New York Botanical 
Garden, in which both kinds of scars were found to occur upon the 
same individual, each in a separate zone. In one cultivated plant in 
particular it was clear that a period of rapid vigorous growth, as 
indicated by a sequence of long-elliptical distant scars, had been 
followed by a period of diminished growth, during which the elonga- 
tion of the stem had proceeded but slowly. The record of the latter 
period was plainly written in the zone of closely set, rounded to 
subhexagonal scars, the shape and position of these obviously having 
resulted from the crowding of the leaves at the apex of the very 
slowly lengthening stem. I have noticed a similar variation in the 
rate of growth in other arborescent species of Cyatheacee, but none so 
pronounced as in Cyathea arborea. 
The age of the larger tree ferns is difficult to determine, and I am 
not aware that any authentic data are available. Certain specimens 
in Jamaica have been reckoned 200 years old, which probably is 
too high an estimate, although many individuals doubtless attain 
an age of at least 100 years, if we may judge from the apparent rate 
of elongation of the upper stem. Growth, however, is more or less 
periodic at some stage in the life history of most large tree ferns, 
depending upon favorable or unfavorable seasons and upon various 
factors of environment; and the only reliable means of arriving at 
the probable age of such individuals is from an extended series of 
observations, over a long period, of plants growing in their native 
environment. 
BRANCHING OF TRUNKS—ADVENTITIOUS GROWTH. 
The upright stems of tree ferns are usually simple, but there have 
been put on record several instances of occasional forking of the 
trunk, and in a few species the tendency is rather pronounced. 
