384 
DR JOHN M‘LEAN THOMPSON ON THE 
shown in the diagrams ( a)-(q ), text-fig. 25, may take place. In slender leaves, 
however, the base of the leaf-trace may not be actually on so divided a footing, but 
may consist initially of two strap-shaped strands. At a point varying between 
4 and 7 inches from the leaf-base, the leaf-trace strands unite, as in text-fig. 26. 
The' main pinna-trace supplies are of extra-marginal origin (text-fig. 27), and it is 
not till the finer distal portion is reached that a marginal supply is encountered. 
The stele and leaf- trace of Gymnogramme japonica are then of an advanced type. 
The stele of Gymnogramme ( Trismeria ) trifoliata is held to be of an advanced 
solenostelic type, and the vascular details of the leaf are decidedly advanced and are 
readily comparable with those of Gymnogramme jajponica. 
The venation of both sterile and fertile pinnae is of an advanced type, with lateral 
dichotomies, and no reticulations (text-fig. 28). 
Sporangia. — In our materials the sporangia are, with few exceptions, inserted on 
the veins (text-figs. 29, 30). At initiation they show a “ simple ” condition from which 
they pass directly to a “ mixed” state, in which interpolation of sporangia commonly 
occurs. The stalk is relatively short, and consists of three rows of cells (figs. 41, 44). 
The annulus is typically vertical, regular, and interrupted by the stalk. There is a 
well-defined stomium. Occasional irregularities occur in the annulus, but these do 
not lead to fundamental disturbances in either the form or position of the annulus 
(fig. 43). 
Spores. — The spores are tetrahedral, and bear on their thin transparent walls 
irregularly distributed bars of thickening (fig. 46). The spore-counts which have 
