OF CEYLON AND INDIA. 
439 
Upon them by that of the vegetati ve organs, or by 
üûeir position upon the latter, without any reference to 
advantages or disadvantages to he derived from it in the 
performance of the functions of the floral organs themselves. 
The only demand made upon them, so to speak, has been 
that they should not cease to set seed ; this they have 
continued to do with success, but in the more dorsiventral 
flowers the chance of cross-fertilization is much diminished, 
and even in some cases lost altogether. 
To turn for a moment to the general conditions of life 
described in the introduction, the total of these, acting upon 
submerged organisms with creeping roots and secondary 
shoots and with subaerial flowers and fruits, would seem 
almost to necessitate more or less of dorsiventrality, and as 
the vegetative organs are in more direct relation to these 
conditions, the effect may be expected to show in them first 
or only ; that it shows also in the floral organs is perhaps 
an accident of the physiological nature of these plants or of 
plants in general. Whether the effect on the floral organs 
is direct, or through the vegetative, we cannot say. It 
would seem perhaps most probable that the dorsiventrality 
of the floAver has not only followed but been determined by 
that of the vegetative organs and the bud-position; it never 
reaches any great structural intensity in cases where the 
dorsiventrality of the vegetative organs or of the position 
of the developing flower is not also highly marked. It 
apparently shows later in the evolution than the dorsi- 
ventrality of the vegetative organs, but it seems gradually 
to work through the series of floral organs, beginning with 
the bracts and spathe and sho wing at last even in the interior 
of the fruit and in the seed. 
It should be especially noticed that the structural 
dorsiventrality of the flowers is accompanied by two 
other phenomena which are always regarded as of high 
morphological and taxonomic importance, suppression of 
parts (here shown in perianth, stamens, carpels, ovules) 
