Jan., 1923] 
SEIFRIZ — GREGARIOUS FLOWERING 
33 
further investigation one would feel convinced on the basis of these facts 
that simultaneous flowering in Dendrobium crumenatum is attributable to 
some environmental influence. 
Before considering what the determining external factor might be—the 
question with which this paper is chiefly concerned—it will be well to con¬ 
sider first how far we are justified in regarding the environment as the 
cause of simultaneity in flowering. It is conceivable that the gregarious 
anthesis of Dendrobium is actually the expression of the heritable disposition 
of the plants, and that the external environment determines only the exact 
time at which the gregarious flowering shall take place. 
If we regard the plants of Dendrobium crumenatum which are growing 
in any one locality as forming their flower buds uninfluenced to any marked 
degree by the external environment, and as developing these buds to a 
definite, and in every case the same, stage of advancement, at which point 
growth is stopped, then we should expect that there will be at any one time 
many resting buds all of the same age. This being true, it is evident that, 
if a stimulus starts all these resting buds growing again at the same time, 
they will all burst into flower on the same day, assuming that the time 
required to cover the final lap of their development is constant in all the 
individuals of the species. This is what Rutgers and Went (5) believe to 
be the explanation of simultaneous flowering in Dendrobium crumenatum. 
The explanation is analogous to that of the ‘‘trigger type” of reaction 
(shock reaction) in animal behavior. The organism is “ primed and cocked.” 
The requisite external stimulus functions merely as a means of releasing 
the ‘‘trigger.” 
If this hypothesis is correct, then the environmental factor in question 
determines merely the exact time when the resting buds shall recommence 
growth, complete their development, and come into flower. Simultaneity 
of flowering rests upon the fact that the resting buds, which are apparently 
aroused to further activity by an environmental factor, are all of the same 
age and all require the same length of time to complete development; that 
is, simultaneity is due to an innate, heritable factor. 
Buitenzorg is renowned for its equable climate. Tropical regions in 
general vary little throughout the year in temperature, but there is usually 
a pronounced seasonal change in moisture. No such alternation of wet and 
dry seasons occurs at Buitenzorg. Where, therefore, the annual precipita¬ 
tion is abundant and so uniformly distributed throughout the year, and 
where other evident environmental factors, such as temperature and light, 
are so constant as at Buitenzorg, it is difficult to appreciate what external 
stimulus might be responsible for the final development and ultimate burst¬ 
ing into flower of Dendrobium buds. 
Burkill (6), from data obtained in the Straits Settlements, comes to the 
conclusion that ‘‘climatic conditions some eight days in advance of the 
flowering are a controlling factor” in the gregarious anthesis of Dendrobium 
crumenatum. 
