378 Farmer arid Hill . — Arrangement and Structure 
seems to be marked a in Kuhn’s 1 figures. The leaf-traces 
also become more complex, and anastomoses take place at 
irregular intervals with the strands which can still be recog- 
nized as the relics of the original siphonostele, as well as with 
one another. Irregularities also begin to become apparent 
as to the relative heights at which the two members of the 
leaf-traces become freed from the plexus of tissue, and a stage 
is thus reached at which the vascular skeleton appears to 
consist of a stout axile strand surrounded by upwardly 
diverging zones of steles which ultimately pass out above 
to the leaves. The complexity and dbscurity is primarily 
due to the commissural strands which connect up the margins 
of the siphonostelic foliar gaps, and the whole arrangement 
is to be correlated with the presence of the bulky parenchyma 
of the stem. 
In the much older stems, such as that described by Met- 
tenius, the principal leaf-traces can still be recognized, in the 
light of what has been said, as being represented by the two 
stout lateral strands of the plexus which travels out to the 
petiole (Mettenius, loc. cit., Taf. Ill, Figs, i* 2, the strands 
lettered a , b). The smaller strands which arise between these 
merely form an extension of that tendency to the formation 
of supernumerary strands which early finds its expression in 
the formation of the commissures already referred to in con- 
nexion with the vascular system of the stem. 
The vascular skeleton of Mar'attia (Figs. 7, 20) is simpler 
than that of Angiopteris , at any rate in young plants of equal 
size. The protostele opens out to form a siphonostele in 
a similar manner in both, but the earlier leaves are not so 
crowded in Marattia as in the other genus. Nevertheless 
the foliar gaps are relatively larger, and hence in transverse 
section the polystelic arrangement of vascular tissue appears 
more striking. The foliar gaps are also much wider than in 
Angiopteris and hence the siphonostele condition is perhaps not 
so obvious, as the impression is gained of anastomoses rather 
than of lack of disunion, when observed in transverse sections. 
1 Loc. cit., Taf. xviii and xix. Figs. 22-24. 
