1922] BLOMQUIST—ANGIOPTERIS 197 
Summary 
1. The general internal structure of the stem of Aazibbiert 
evecia consists of two main regions, the cortical and central vascular. 
The relatively thick cortex is traversed by leaf traces and roots. 
The central region consists of a vascular strand which appears 
crescent-shaped in cross-section and is imbedded in a central 
parenchyma tissue. This strand gives off root steles and leaf 
traces. In addition, commissural and resgeee! strands appear in 
the central region. 
2. The leaf traces are given off from one edge of the central 
strand, and this contribution is always from the same edge in the 
same plant. On about the same level that the leaf trace leaves 
the central strand a root is attached on the outer side of the other 
edge. The contribution thus made to the leaf traces is made good 
on the opposite edge in two ways, by an increase in the vascular 
tissue on the edge itself, and by the addition of commissural strands. 
3. The commissural strand originates from the free edge of the 
leaf trace after the latter is freed from the central strand, and 
passes to the opposite edge of the central strand and fuses with it. 
4. By a continual loss of tissue from one edge and an addition 
on the other the central strand assumes a spiral condition. This 
condition is due to the spiral succession of leaves. 
5. In the older stages a medullary strand appears on the inner 
side of the central strand opposite the upper level of a root junction. 
This crosses the central parenchyma tissue and fuses with the 
commissural strand before the latter has fused with the central 
strand. After fusion has taken place, the medullary strand passes 
_ upward on the inner side of the central strand, fused to the latter 
but retaining its identity, until the root junction has been cleared, 
when it frees itself and repeats its course across the central paren- 
chyma. 
6. Each leaf trace is definitely related to one root. The root 
which appears almost opposite a leaf trace corresponds to the next 
leaf above. In the early stages each leaf trace appears directly 
above its corresponding root; but in the later stages the leaf trace is 
displaced to the right or left, as the case may be, of its corresponding 
root, due to the spiral condition of the central strand. 
