252 Contribution to a Statistical Study of the CrucifercB 
when the flower opens but, along with small nectaries at the base of the stamens, 
serve as an attraction for insects whose visits are essential for cross-fertilisation. 
The reproductive organs of what is regarded as the typical cruciferous flower 
consist of (1) the gynsecium which is composed of two carpels and (2) the androecium 
which is composed of six stamens. The stamens are delicate structures and do not 
hold an isolated position in the flower. When in the bud and immature they are 
subject to external influences, for example, (1) they might be shrivelled up by the 
heat of the sun, (2) they might be blasted by rain or wind or (3) they might be 
attacked by herbivorous insects, so that the protective perianth plays an important 
part in flower economics. Now what does an increase in the number of stamens 
imply ? It is obvious that if the number of stamens is increased the total vohime 
occupied by the reproductive organs is increased and consequently a tax is put 
upon the protective organs if they are to fulfil their function adequately. If the 
perianth does not respond to this tax from space considerations, the reproductive 
organs stand a small chance of ever fulfilling their function, so that one would 
naturally expect that variation of some kind in the perianth would follow variation 
in the reproductive organs. 
Another important point which must never be lost sight of when interpreting 
the statistical results is the symmetry of the cruciferous flower. The calyx consists 
of tw"o whorls each with two sepals; the corolla of one whorl of four petals and the 
androecium of tvvo whorls of stamens, the outer having two members and the inner 
four members (see Plate I, fig. 7). Consequently a cruciferous flower is bilaterally 
symmetrical only on that vertical plane which passes through the division wall of 
the carpels, between each of the pairs of stamens in the inner whorl, between two 
petals on either side and through the middle of the outer pair of sepals. This 
plane may be referred to as the "plane of symmetrical division." Owing to the 
fact that the corolla consists of only one whorl, the outer whorl of the calyx 
corresponds in position to the inner whorl of the androecium, and the inner whorl 
of the calyx to the outer whorl of the androecium. 
From a study of the Means and Standard Deviations of the various organs and 
constituents we arrive at the following conclusions : 
Calyx. (1) The greatest approach to constancy in number in the whole 
flower is in the inner whorl of the calyx. 
(2) There is a significant difference between the means of the two whorls. 
(3) There is much greater variability in the outer than in the inner whorl of 
the calyx and on an average it possesses fewer sepals. 
(4) There is a tendency towards a reduction from type in the number of 
sepals in the calyx. 
Corolla. (5) There is a tendency towards a reductimi from the accepted 
typical number in the number of petals in the corolla. 
