24 Sargant . — Theory of the Origin of Monocotyledons 
two traces. These traces are inserted on those of the cotyle- 
don at the first node (PI. Ill, Fig. 3). 
At this point the transition to a root-like structure has 
already begun in the stele. The protoxylem of each main 
bundle is branching in two directions. The branches towards 
the top of the section have united with each other : those 
which have turned in the opposite direction are distinct, 
and have each joined a group of plumular xylem (PI. Ill, 
Fig- 3 )- 
Below the node there are two crescent-shaped xylem 
masses, each crescent partly encloses a very well-defined 
circular group of phloem (PL III, Fig. 4). The extended 
protoxylem covers the convex surface of either crescent, 
but though the crescents lie close together and present their 
convex outline to each other, the protoxylem elements of the 
two bundles are united only at one point near the top of 
the stele. 
Very little below this, the two massive xylem crescents 
meet in the centre of their convex surfaces, and the proto- 
xylem sheath on both sides is broken in the centre. There 
are now four protoxylem rays stretching out towards the 
horns of the crescent. They are united in pairs to form 
the groups px . 2 and px. d in Fig. 5, PI. III. The whole 
structure is that of a diarch root with the protoxylem rays 
extended tangentially. 
So far the transition is essentially that characteristic of the 
Tulipeae (Diagram V). Two cotyledonary traces have formed 
a diarch root-stele according to Van Tieghem’s type 1, that is, 
by branching of the xylem and fusion of adjacent branches. 
But in F. imperialis the process does not stop there. The 
protoxylem elements creep round the horns of the crescents 
until they meet on either side and form two groups external 
to the two phloem-masses. Each phloem-mass breaks into 
two (PL III, Fig. 6), and the root is then tetrarch. In a 
similar way it becomes first hexarch and then heptarch a little 
lower down. 
This variation on the type is doubtless due to the persist- 
