404 MR. W. AND MISS A. BATESON ON FLORAL VARIATIONS 
of the two rows to each other is about 90°. This process is 
called by gardeners “making a face,” and a perfect “face” 
constitutes a special beauty in these flowers. In addition to 
this horizontal rotation, each flower, instead of looking upwards, 
bends over so as to face outwards from the axis. This change 
of direction is associated with unequal growth of the different 
segments of the perianth, by which some of them become 
larger than others. The number of the segments which are 
thus distinguished from the rest varies greatly, and the degree 
to which this differentiation proceeds is also very different in 
the various kinds. As the result of this process of differentia- 
tion the perianth comes to be partially divided into a posterior 
portion, of which the segments are large, and an anterior lip, 
having one to three small segments. In some flowers this division 
is striking, but in others there is no very definite distinction 
between the anterior and posterior limbs of the perianth. In 
connexion with this change of position of the flower, the radial 
symmetry is lost, but as the flower becomes thus irregular a 
marked bilateral symmetry supervenes. The fact to which we 
now wish to draw attention is this: that the new bilateral sym- 
metry does not in all flowers develop about the same plane, but 
it may, on the contrary, be produced in one of two chief ways. 
In the first of these types the irregular perianth is symmetrical 
about the plane of the floral axis; and from examination of the 
diagram it will be seen that this plane falls in such a manner as 
to bisect the posterior segment (6) of the inner perianth and the 
anterior segment (3) of the outer whorl. This gives a flower of 
the form which we have called our first type, and in it the petals 
2 and 4 at least are modified, the petal 3 sometimes being marked 
like them. 
In the flower formed on Type II. the symmetry is disposed about 
a different plane, which is not that of the floral axis, but is the 
plane of that segment of the perianth which stands next to the 
segment which is in the plane of the floral avis. It thus happens 
that the middle plane of the flower bisects the segments 5 and 2, 
thus falling anteriorly between two segments of the outer whorl. 
This is the condition in our second type of flower. In it either 
the segment 2 alone may be modified and unguiculate, or the 
segments 1,2, and 3 may all be thus modified. The attitudes 
which the stamens assume depend upon the plane about which 
the symmetry is developed; the difference between them has 
already been described. 
