Vascular Anatomy of Platycerium. 319 
In the leaf-trace, the outer ring of strands is derived from the 
dictyostele of the axis, while the medullary strands in the petiole 
arise either from the medullary strands of the axis or by splitting off 
from the outer petiolar ring. As before, a meristele closes the gap. 
In a young plant of this species, there appeared in the earliest 
stage to be one strand with a core of xylem and parenchyma, a 
haplostele, surrounded by phloem and pericycle. Very soon, 
however, phloem and parenchyma appear internally and the original 
strand is cut into two meristeles by an intrusion of sclerenchyma, of 
which the ground-mass of the axis is composed. These two 
meristeles almost immediately divide again, so that four meristeles 
are present of practically the same nature as those in the mature 
plant (Fig. 5, 1-4). The solenostelic stage appears to be omitted. 
Two of the meristeles unite to form a long dorsal meristele, which 
persists for some time but later splits into a number of meristeles. 
The meristeles are constantly uniting and dividing so that the 
identity of one is not maintained for any length of time. The first 
indication of the accessory medullary strands, such as are found in 
the older stem, is seen in the splitting of a small bundle from one 
of the meristeles (Fig. 5, 11-13). This little strand remains 
independent for a very short time and soon joins a neighbouring 
meristele, only to break away again later as an internal strand 
(Fig. 5, 14-17). 
The leaf-trace has its origin in one meristele which soon 
divides into two strands, one of which sub-divides into two 
immediately (Fig. 5, 17-20). However, one of these strands joins 
one of the meristeles of the stem, and the leaf-trace really consists 
of two strands only, which divide to form the three bundles of the 
petiole (Fig. 5, 20-24). After this leaf-trace has been given off, one 
of the outer meristeles divides into two and the first permanent 
medullary bundle is formed (Fig. 5, 25). This bundle, with two 
other bundles which have split off from the outer ring, form an 
internal ring (Fig. 5, 26-28). As in the older plant, these inner 
bundles unite with each other and also with the outer meristeles. 
The leaf-trace of the next leaf appears to be formed by two of the 
outer meristeles, which elongate and extend into the leaf. One of 
the medullary strands unites with the outer ring and passes into the 
petiole (Fig. 5, 30-34). 
It is difficult to make a summary of these results, since the 
structure, particularly in the matter of the behaviour of the 
medullary bundles is somewhat exceptional. It is to be noticed 
