34 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
The data of Burkill consist in the dates of simultaneous flowering of 
the pigeon orchid for four years (twenty-seven flowering periods in all) and 
the daily rainfall figures for these years. When the two groups of data are 
arranged in a table, it is to be noticed that in most instances the precipitation 
is unusually heavy on the eighth (sometimes the seventh or ninth) day 
before each anthesis. Especially evident does this fact become when one 
considers the total rainfall for each series of days preceding all th$ flowering 
periods. The total for the eighth series of days is greater than that of 
any other. But among the rainfall data preceding each flowering date 
there are some prominent exceptions. These undoubtedly caused Burkill 
to conclude that 
It is not probable that the volume of the rain which falls exercises any direct influence 
on the flower buds; but it is quite probable that the changes in temperature accompanying 
heavy rainfall . . . determine the occurrence. 
Wishing to ascertain if the theory of Burkill is supported by the relation 
between rainfall and the flowering of Dendrobium crumenatum at Buitenzorg, 
Java (where climatic conditions differ considerably from those prevailing 
at Singapore), I have compared the days of flowering of the orchids and 
the daily rainfall for twenty-seven days preceding these flowering periods 
at Buitenzorg. These data are arranged in table I. 1 
If we study the table, the first evident and striking fact is that, of the 
precipitation totals of the various days which precede each flowering date, 
that of the eighth—the day on which Burkill found the total rainfall to be 
at the maximum—is here also the greatest. The total rainfall occurring 
on the eighth day previous to all the flowering dates is five ninths greater 
than that of the next highest. Thus, at the very outset, do we have strong 
support of Burkill’s hypothesis. If we examine the table more critically, 
further favorable evidence is found. 
In several instances prolonged dry periods are broken by rainfall on the 
eighth day before a flowering date ( e.g ., Oct. I, 1895; Aug. 25 and Sept. 23, 
1896; and Aug. 24, 1919: a shorter dry period is broken on the eighth day 
preceding the flowering on Nov. 13, 1896, and on Sept. 3, 1919). It will be 
noticed that in each of these cases the amount of flowering was abundant. 
In some instances the heavy rainfall occurred a day later or two or three 
days earlier. These slight divergencies can be regarded as variations of 
not sufficient greatness to affect materially the theory. Other exceptions 
exist, however, which are more disturbing. Thus, on Sept. 7, 1894, April 8, 
and Dec. 10, 1895, very heavy rainfall occurred on the fourteenth or fifteenth 
day preceding flowering. One wonders why these precipitations (and even 
that taking place on the twenty-seventh day preceding Oct. 17, 1894, for 
example) did not occasion gregarious flowering in the orchids eight days 
1 For the dates of blossoming of Dendrobium crumenatum I am indebted to Dr. J. J. 
Smith, Chief of the Buitenzorg Herbarium. For the precipitation data my thanks are due 
to the Meteorological Observatory of Batavia, Java. 
