Feb., 1923] 
SEIFRIZ — CAUSES OF GREGARIOUS FLOWERING 
IO9 
solution of starch, etc.—some are undoubtedly susceptible to environmental 
factors. Furthermore, the same phenomenon varies in different plants in 
the readiness with which it can be influenced by surrounding conditions. 
Thus, the winter’s rest in some plants is easily altered, in others it can not 
by any known artificial means be broken. Klebs first clearly showed 
experimentally that periodicity in plants can be disturbed. In this lies 
his contribution to biology. But when Klebs would have us believe that 
all the activities of plants are to some extent determined by the outer 
world, we question his right to do this in the face of his own experiments 
since he found certain plants which could not be aroused from their winter’s 
rest (15). 
But even in those cases in which the normal periodicity can be disturbed, 
the question arises whether or not the mere ability to alter the normal 
rhythm of growth by changing the external environment is an indication 
that this periodicity is actually the direct result of an environmental rather 
than of a germinal factor. There are some striking instances in which the 
normal alternation of growth and rest is upset but the plant suffers in 
consequence. Disturbing the usual growth rhythm results in weakening 
the plant’s vitality. An excellent illustration of this exists at Tjibodas, 
Java, where there is a small apple tree growing in the acclimatization 
garden in the mountains. This temperate-zone tree has been growing in 
the tropics for some twelve years or more, in a climate which has no pro¬ 
nounced seasonal change. Its normal periodicity of growth and rest has 
been disturbed but not done away with. The tree is undersized (four feet 
high) and has never borne fruit. It stands there an unhappy specimen, 
with, when I saw it, one branch in full foliage, another without any leaves 
at all, and still another with well-developed buds. It seems to be having a 
sad time trying to exist in a seasonless climate with an inherent periodicity 
of growth and rest manifesting itself at different times of the year on different 
branches. The periodicity is there. The seasonal cycle of temperate 
regions would have determined when the rest and growth periods should 
occur. In a tropical climate this seasonal guidance is lacking and the 
normal rhythm of growth and rest is disarranged, but the inherent perio¬ 
dicity is still evident. 
The fact that the winter’s rest in plants can in many cases be disturbed 
has led other workers than Klebs to come to rather far-reaching conclusions. 
Thus Howard, as a result of some very extensive work on the treatment of 
dormant woody plants for forcing them into growth, concludes that “all 
of these forms of rest are caused by unfavorable external conditions” (9, p. 5). 
Just what the unfavorable conditions are which cause all kapok trees 
{Ceiha pentendra) simultaneously to become completely defoliated each year 
at Buitenzorg, where there is no pronounced seasonal change, it is difficult 
to see. Even more striking is the case of Ceiba (C. occidentalis ?, the silk- 
cotton tree) in Jamaica which annually loses all its leaves, but not simul- 
