218 Contribution to a Statistical Studtj of the Cruciferce 
2. Morphology of the flower. 
The typical flower consists of six whorls, made up in the following manner : 
(a) Calyx 2. " 
{h) Corolla 1. 
(c) Androecium 2. 
(d) Gyna?cium 1. (Plate I, fig. 1.) 
(a) Calyx. This organ is composed of two whorls each consisting of two 
sepals. The outer pair arise at one level on opposite sides of the flower and are 
inserted on a slightly lower plane than the inner pair; they are parallel to the 
plane of compression of the gynaecium. The inner pair are also situated opposite 
one another but in a plane perpendicular to that of the outer pair; they are thus 
at right angles to the plane of compression of the gyna^cium. These whorls are 
denoted on Plate I, fig. 1, by the Roman numerals I and II respectively. 
(6) Corolla. This organ consists of four petals all inserted at one level and 
altei'nating with the position of the sepals ; they thus constitute a single whorl. 
(See III, Plate I, fig. 1.) 
(c) Androecium. Six stamens form the androecium ; they arise at two different 
levels and thus constitute two separate whorls. The outer whorl, which is lower 
down, consists of two stamens which are shorter than the others and corre- 
spond in position to the inner sepals. The inner whorl consists of four stamens, 
arranged in pairs which correspond in position to the outer sepals. (A reference 
to the figure (Plate I, fig. 1) in which the two whorls are marked IV and V 
respectively will make this clear.) 
id) Gyncecium. This organ consists of two carpels forming the sixth or 
innermost whorl. (See VI, Plate I, fig. 1.) 
It will be seen from the foregoing description that the order of the six whorls 
here detailed is that in which they would be found were we to strip the flower of 
its components at the different levels consecutively from below upwards. It is 
also the order in which we would find them, passing from the outside to the 
centre, were we to cut a transverse section through the flower. 
Another point, however, which is not so obvious but one which has special 
interest in our study, is the fact that this is also the order in time of development. 
The actual sequence in which these constituents of the flower appear in the 
bud is therefore : 
I. Outer whorl of Calyx (Sepals). 
II. Inner whorl of Calyx (Sepals). 
III. Corolla (Petals). 
IV. Outer whorl of Androecium (Stamens). 
, V. Inner whorl of Androecium (Stamens). 
VI. Gyngecium (Carpels). 
