IMBRICATIVE STIVATION. 707 
first case two opposite parts are wholly external, and the other 
two opposite parts are wholly internal (Fig. 113), as in the calyx 
of cruciferous flowers. This is the case of opposite decussate 
leaves. In the second case one part is external, one internal, and 
Fig. 113. Fig. 114. 
Fig. 115. Fig. 116. 
3+ a — 
_ the other two intermediate. In this case there are two varieties, 
a according as the internal part. is opposite or adjacent to the ex- 
_ ternal part. When the internal part is adjacent, there is an evi- 
dent spiral arrangement. Numbering the parts 1, 2, 3 and 4, 
: Fig. 117. Fig. 118. 
i Š 
eo a {- A 
the spiral makes one turn to the right (Fig. 115), or to the left 
(Fig. 116), according as 4 is on the right or left of 1. This is 
i the common arrangement of the petals of cruciferous flowers. 
The internal part may sometimes be seen opposite (Fig. 114) in 
l; 
