THE LEAF-TRACE IN SOME PINNATE LEAVES. 
23 
strands, scattered respectively in the centre and round the periphery of the rachis. 
The pinnae are inserted on cushions, to which the adjoining strands of the leaf-trace 
give off a line of large strands, preceded, accompanied, and followed by an indefinite 
number of the small peripheral strands, which pass out in no regular sequence but 
quite sporadically. 
In these three examples from the Palms there is given off from the portion of the 
leaf : trace which is nearest to the pinnae a series of larger and smaller strands, which 
are nipped off from the central and peripheral series respectively of the leaf-trace 
strands. 
Philodendron Selloum, C. Koch. 
In Philodendron Selloum, C. Koch, a large-leaved Aroid with two large basal 
pinnae and an imperfectly-segmented laminar region beyond them, the strands of the 
leaf-trace are very numerous and are scattered at more or less equal distances from 
one another through the tissue of the petiole and- rachis. The basal pinnae are 
inserted at the same level, and are supplied from the peripheral, intermediate, and 
central regions of the rachis on the sides directed towards them. Many strands come 
from the periphery and from the intermediate region, and a few from the centre of 
the rachis. 
Philodendron with its large pinnae draws on a greater area of the leaf-trace than 
do the Palms, and the central strands of the leaf-trace, which in the Palms are un- 
affected by the departure of the lower pinnae, are here employed in some degree in 
connection with the first pair of pinnae. 
These examples from the Monocotyledons show in the outlines of the leaf-trace 
and in the method of supplying the pinnae from it no resemblance to the Ferns or the 
Cycads. The portion of the leaf-trace nearest to the pinnae gives off the pinna-traces 
from its strands by simple fission ; there is no allocation of supplying duties to one 
series, of reinforcing duties to another, such as we find so prominently among the 
higher Ferns and the Cycads. 
The less rigid organisation of the leaf-trace and the less stereotyped method of 
forming the pinna-trace are probably related to the system of scattered vascular 
strands which is found in the Monocotyledons. 
Before proceeding to consider the features of the leaf-trace in the Dicotyledons 
we may summarise the results of the examination of the leaf-traces of the groups 
already examined. 
In the Ferns the outline of the leaf- trace .is dependent partly on the length of the 
leaf, partly on the size and number of the pinnse, and partly on the systematic 
position of the Fern. In a close circle of affinity the adaxial portion of the leaf- trace 
is unaltered, but the size of the leaf may affect the development of the abaxial 
curve. 
The method of giving off the part of the pinna-trace which comes from the adaxial 
