STRUCTURE AND AFFINITIES OF LEPIDOSTROBI. 447 



Fig. 6. The portion marked x in fig. 5, magnified equally with fig. 4. 



lig. 7. A group of spores from fig. 5, very highly magnified, exhi- 

 biting their characteristic trisection by opaque lines. 



Fig. 8. A smaller group of more advanced spores from fig. 3, still 

 more highly magnified. 



Fig. 9. Individual spores selected from figs. 4 and 6. They are ge- 

 nerally tetrahedral bodies, divided into three by broad transparent 

 spaces. The youngest, a, b, c, are immature, and present spurious pro- 

 jections at their three angles, which spines are continuous with the 

 transparent spaces and acute, deformed by prolongations of the con- 

 tiguous apices of the three sporules comprising the spore. Letter d 

 indicates a more mature spore, with the spines very nearly obliterated. 

 At letter e is a still more matured spore, whose angles are rounded, and 

 in which the transparent spaces are broader, indicating that the spore 

 has all but broken up into three sporules. 



Fig. 10. A vertical section, of the natural size, of a portion of the 

 cone, Plate 4, fig. 2 a. In this the tissues of the axis are preserved. 

 This axis is hollow in the centre from the obliteration of the once cel- 

 lular (?) tissue filling it. 



Fig. 11. A semi-diameter of the axis of fig. 10, showing at a the 

 tubes of vascular tissue, which once formed a continuous zone round 

 the pith ; b, the system of vascular tissue exterior to the former, which 

 gives off the bundles c to the scales of the cone. The arrangement of 

 these tissues will be best observed by referring to the wood-cut of these 

 parts in Lepidodendron, at p. 436 of this volume. 



Fig. 12. Tubes of the perpendicular vascular tissues a, of fig. 11. 

 These are marked with horizontal rings, sometimes free, at others anas- 

 tomosing at various points. 



Fig. 13. Slender tubes b, of the vascular system, c of fig. 11, sup- 

 plying the scales. They are surrounded by cellular tissue d, formed of 

 elongated utriculi. The tubes are much more delicate and slender than 

 those of the other system of vessels. 



Plate 6. Horizontal sections of the cones, Plates 3 and 4. 



Fig. 1. Slice of the mature, a, and immature, b, cones, seen in 

 Plate 3, fig. 2. 



Fig. 2. A portion of the coaly bark close to the surface of the Lepi- 

 dodendron, showing its cellular tissue. 



Fig. 3. A highly magnified portion of the cone, fig. 1 a, showing a 

 section of the apex of one scale, with several others imbricating over it. 



Fig. 4. Still more highly magnified view of a portion of a similar 

 scale, edged by the walls of a sporangium c. The scale is chiefly formed 

 of cellular tissue, enclosing in its centre a mass of vascular tissue a, 

 which turns up to the ascending apex of the scale at b. 



