THE GREGARIOUS FLOWERING OF THE ORCHID 
DENDROBIUM CRUMENATUM 
William Seifriz 
(Received for publication April 3, 1922) 
Whenever a number of individuals of the orchid Dendrobium crume- 
natum Lindl. occur within the same general locality the plants flower simul¬ 
taneously. 
Such gregarious flowering is met with in other plants: for example, in 
certain bamboos such as Bambusa arundinacea (1), Phyllostachys puberula 
(2), and Chusquea abietifolia (3). There are, however, two striking differ¬ 
ences between the simultaneous flowering of the orchid and that of bamboos. 
First, in the latter case the flowering is rhythmic. In bamboos which 
exhibit rhythmic sexual periodicity the time between periods of flowering, 
i.e., the life of the plant, is about thirty-two years (3, 4). In Dendrobium 
the periods between flowering dates vary from a few days to several months. 
A glance at the dates of flowering in table 1 is sufficient to reveal the fact 
that there is no rhythmic periodicity here. The second striking difference 
between the gregarious flowering of orchids and that of bamboos is that in 
the latter case all the individuals of a bamboo forest are of the same age, 
while among an assemblage of orchids the individuals may be of quite 
different ages. In the case of bamboos there is accordingly good reason to 
regard the sexual periodicity as the expression of an innate, heritable 
character (3). The lack of rhythm in the flowering of the orchid and the 
differences in the ages of the plants which flower gregariously suggest that 
simultaneity here is possibly due to an external factor. The following 
additional observation tends further to support this belief. 
Among the specimens of Dendrobium crumenatum in the Botanic Gardens 
at Buitenzorg, Java, there are plants collected from nearly all parts of the 
Dutch East Indies, from Riouw (near Singapore), from Sumatra, Java, 
Borneo, Celebes, and Ambon (a small island at the eastern end of the 
archipelago). These plants, shortly after being brought to Buitenzorg, all 
flowered on the same day, if they flowered at all; yet in their native habitats 
the flowering periods of the plants do not at all coincide. Thus, orchids 
growing in the virgin mountain forests flower on different days from those 
in the lowlands. Plants growing at two stations but three kilometers apart 
may differ in their times of flowering by one or two days. But wherever 
their original home and whatever the date of flowering there, the plants, 
when assembled in one locality, flower simultaneously with each other and 
with the plants which have grown in that locality from youth. Without 
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