360 
PROFESSOR W. WILLIAMSON ON THE ORGANIZATION 
Fie’. 28. T ang ential section across the node of a decorticated Calamite, about 1‘25 
in diameter, and with a vascular cylinder about ’25 in thickness, 
c. Primary medullary rays, f Primary vascular wedges, to. Small 
lenticular cellular (?) areas, apparently identical with fig. 23, to. In the 
middle of the section is a transverse section of a small emerging 
branch, having a central cellular medulla, surrounded by a cylinder of 
radiating lamellae of vascular tissue. Enlarged 20 diameters. 
PLATE 20. 
Fig. 29. Part of a tangential section of a node of the same Calamite as fig. 28. 
The cellular area, to, is the medullary extremity of a branch intersected 
transversely, and a similar section of the peripheral part of which is 
almost identical with fig. 26. to', to'. Enlarged secondary medullary rays. 
Enlarged 33 diameters. 
PLATE 21. 
Fig. 30. A Calamite in shale with the base of a large lateral branch. Natural size. 
Fig. 31. Lower extremity of the sandstone cast of the fistular medullary cavity 
of a Calamite with two verticils, l, V , of the casts of the infranoclal 
medullary canals passing through the decomposed carbonaceous matter 
of the vascular zon e,f f Slightly enlarged. 
Fig. 31a. Vertical section through fig. 31b intersecting the two fistular medullary 
canals, a. Medullary canal of primary stem. a. Medullary canal of 
branch, f Vascular zone of primary stem. Vascular zone of branch. 
f". Vascular area intermediate between the two fistular medullary 
canals, a and a , fig. 31. Two-thirds natural size. 
Fig. 31n. Transverse section of a decorticated Calamite giving off obliquely a lateral 
branch, a. Medullary canal of primary stem. a. Medullary canal of 
the branch to. f Vascular zone of primary stem, f . Vascular zone 
of branch with its primary vascular wedges separated by the primary 
cellular medullary rays. Two-thirds natural size. 
Asterophyllites. 
Fig. 32. Obliquely transverse section of an Asterophyllites passing through a node. 
c. Primary vascular axis. d. Exogenous vascular zone, consisting of a 
single layer of vessels, g. Space left vacant by the disappearance of the 
inner bark. k. Outer bark. 1. Vacant canals left by the destroyed 
vascular bundles of a corresponding number of verticillate leaves. 
to, to.' Leaves, x. Triangular vascular bundle going off to a lateral 
branch. 
