THE ORCHIDS OF NEW ENGLAND. 83 
developed. The lowermost division (lowermost in the accom- 
panying figure), and the two upper ones form the lower sertes 
or verticil, or, as it would be called in other orders, the calyx. 
The lower leaf (lower as before noted), if the 3 were drawn 
out on a stem as real green leaves, would be the upper or 3d in 
the cycle, and we see that it has begun to change its form. The 
next drawing in of the spiral twist, which has resulted in 
another cycle or verticil of 3 leaves brought down to one 
plane, has ended by bringing the upper normal leaf, and the 
most changeable, as we have already seen, just opposite to 
where the twisting of the lower verticil ended. . . . In 
other Orchids . . . another twist takes place in the 
ovarium just as the petals are about to open and after all the 
twisting so far described has been done, and the result is that 
the lip (which in our flower is the uppermost leaf of the 2d 
verticil) assumes the position of the lowermost part of the 
flower. In Calopogon the extra twist has not occurred, and the 
result of this limited torsion is that the lip forms the upper 
instead of the lower part of the flower.” 
Some Orchids have the foot-stalk twisted instead of the 
ovarium, Darwin says. In either case, “from slow changes in 
the form or position of the petals, or from new sorts of insects 
visiting the flowers, it might be advantageous to the plant that 
the labellum should resume its normal position on the upper 
side of the flower, as is actually the case with Malaxis paludosa 
and some species of Catasetum, etc. This change . . . might 
be simply effected by the continued selection of varieties 
which had their ovaria less and less twisted; but if the plant 
only afforded varieties with the ovarium more twisted, the 
same end could be attained by the selection of such variations, 
until the flower was turned completely round on its axis.” 
Thus in Malaxis paludosa, “ the labellum has acquired its pres- 
ent upward position by the ovarium being twisted twice as 
much as usual.” 
