a2? HETEROMORPHY. 
are opposite in each verticil and crossed in the two 
successive ones. ‘The stem is four-angled, each angle 
haying a nerve. LHach of these nerves, springing from 
the origin of a branch in one whorl, terminates in the 
interval which separates the point of origin of the two 
branches in the whorl next above it. In the deformed 
stem one of the nerves corresponds to the insertion of a 
branch, its neighbour is in the adjoming vacant space ; 
hence it results that four nerves correspond to two 
branches and to two consecutive interspaces, and hence 
the analogy between a single normal internode provided 
with its two branches and its four nerves. What con- 
firms this inference is that the nerve, which begins 
at the point of origin of a branch, after making one 
spiral turn round the stem, terminates in the interval 
that separates the two following branches, just as in a 
branch of the normal stem it ends in the upper whorl 
between the two next branches. ‘The torsion, then, in 
this Galiwm caused the separation of the two opposite 
branches of the same verticil, and placed them one 
above another, and this being reproduced in all the 
whorls, all the branches come to be arranged on the 
same longitudinal line. The leaves are susceptible of 
the same explanation; they are inserted in groups of 
three or four in one arc round the origin of each 
branch. In the malformation each series or group of 
four leaves, with its central branch, is equivalent to 
half a whorl of the natural plant with its amllary 
branch. In other words, the malformation consists in 
a torsion of the stem, which separates each whorl 
into two distinct halves; these half-whorls, with their 
axillary branches, are placed on a single longitudinal 
series one above another. This case 1s quoted at some 
length, as it is an admirable example of a very common 
form of malformation in these plants. 
In some parts of Holland where madder is culti- 
vated a similar deformation is particularly frequent. 
The leaves, however, are not always grouped im the 
way in which they were described by M. Duchartre, 
