Origin and Development of the Compositee. 13Q 
Bijugate Types. In the normal Fibonacci phyllotaxis a single 
genetic spiral can be traced. This, however, is quite a subjective 
phenomenon. Other cases occur with two or more genetic spirals 
and these are described as bijugate or multijugate. Where the 
capitula are bijugate the phenomenon usually extends to the 
vegetative parts and the leaves then occur in pairs which may or 
may not decussate. 
This bijugate phyllotaxis is amenable to the same geometrical 
treatment by means of curve systemsof the series 2(5 + 8) or (10+16) 
etc., (cp. 1, Pt. II, p. 166). Bijugate systems occur rarely in 
HeliantJius annuus and are also normal in the terminal capitula of 
some species, e.g., Silphium perfoliatum, where the lateral capitula 
show the normal Fibonacci phyllotaxis. Other cases in the 
Composite which are sometimes bijugate are Arnica, SpilantJies 
and Zinnia. 
B. Phyllotaxis of the Leaves. 
Wydler (29) and Reinecke (21) give numerous data of the 
phyllotaxis of the vegetative parts of the plant. Cassini (I, 18) 
confined his attention with very excellent results to the floral 
characters of the family. Bentham (I, 7) gives a short and not 
very accurate analysis of the distribution of alternate and opposite 
leaves in the various tribes. 
That opposite leaves are primitive in the Dicotyledons is fairly 
obvious from the condition of the embryo and is proved by 
Henslow (8). The addition of one extra member, giving a (2 + 3) 
system instead of a (2 + 2) system is considered by Church to take 
place very readily, so that an alternate phyllotaxis probably arose at 
an early stage in the history of the Dicotyledons (cp. Henslow, 
loc. cit ). 
The fact that opposite leaves are primitive for the Dicoty¬ 
ledons is, therefore, quite irrevelant, and the evidence within the 
Compositse is in favour of alternate leaves being the primitive 
condition for the family. The probable origin of the Compositae 
from the Lobelioideae, where the leaves are practically always 
alternate, furnishes further evidence. 
As the distribution of these two types of phyllotaxis follows 
the general phyletic lines already laid down, a brief account of the 
variation will add to the cumulative effect of the evidence for these 
phylogenetic conclusions. 
As before, the Senecioninae show the primitive type (alternate) 
with variation showing reversion to the type which doubtless was 
