2 ARRANGEMENT OF ORGANS. 
modes of arrangement, dependent, as it would seem, on 
their simultaneous or on their successive development ; 
thus, if two leaves on opposite sides of the stem are 
developed at the same time, we have the arrangement 
called opposite; if there are more than two, the dispo- 
sition is then called verticillate or whorled. On the 
other hand, if the leaves are developed in succession, 
one after the other, they are found to emerge from the 
stem in a spiral direction. In either case the leaves 
are arranged in a certain regular manner, according to 
what are called the laws of Phyllotaxis, which need not 
be entered into fully here; but in order the better to 
estimate the teratological changes which take place, it 
may be well to allude to the following circumstances 
relating to the alternation of parts. The effect of this 
alternation is such, that no two adjacent leaves stand 
directly over or in front one of the other, but a litle 
to one side or a little higher up. Now, in the alternate 
arrangement the successive leaves of each spiral cycle 
alternate one with another till the coil is completed. 
For the sake of clearness this may be illustrated 
thus :—Suppose the spiral cycle to comprise five leaves, 
numbered 1, 2, 3, 4, 5, then 2 would intervene between 
1 and 3, and so on, while the sixth leaf would be 
the commencement of a new series, and would be 
placed exactly over 1. This arrangement may be thus 
formularised : 
8 9 10 
3 + 5 
In the verticillate or simultaneous arrangement of 
leaves the case is somewhat different. Let us suppose 
a whorl of eight leaves, surmounted by a similar whor] 
of eight. In such a case it will generally be found 
hed, 
Do oN 
