SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 627 
showing two lobes, one of which is again subdividing, to., wall ; tap , tapetum ; col. a ; col. b ; col. b', the 
three divisions of the columella. x 20. (Slide No. 2457.) 
Fig. 64. Sporangium in transverse section lying beside a longitudinal section of a stem, to., wall; sp., 
spores; col., columella. x 20. (Slide No. 2457.) 
Plate X. 
Hornea Lignieri, Kidston and Lang. 
Fig. 65. Portion of transverse section of a sporangium of Hornea. ep., epidermis ; m.l., middle layers 
of wall; tap., tapetum; sp., spores; col., columella. x 60. (Slide No. 2458.) 
Fig. 66. Transverse section of a sporangium showing the thickened epidermis, ep., epidermis ; m.l., 
middle layers of wall; tap., tapetum; col., columella. x 20. (Slide No. 2456.) 
Fig. 67. Portion of wall of sporangium in fig. 66 more highly magnified, ep., epidermis with thickened 
outer walls; m.l., perished middle layers of wall; tap., tapetum. x 60. (Slide No. 2456.) 
Fig. 68. Fragment of the epidermis of a broken sporangium showing the thickening of the outer walls 
extending on to the lateral walls. x 60. (Slide No. 2439.) 
Fig. 69. Portion of one of the sporangia in fig. 58 showing the columella in longitudinal section, w., 
wall ; sp., spores in the dome-shaped cavity lined by the tapetum (tap.). x 60. (Slide No. 2454.) 
Fig. 70. Portion of a tangential section of a sporangium to show the persistent tapetum. w., wall ; 
tap., tapetum. x 60. (Slide 2451.) 
Fig. 71. Spores in tetrads around the columella (col.). x 105. (Slide No. 2459.) 
Fig. 72. Mature spores in sporangium, col., columella. x 160. (Slide No. 2456 ) 
We again gratefully acknowledge our indebtedness to the Executive Committee of the Carnegie Trust 
for a grant to defray the expense of the plates illustrating this memoir. 
TRANS. ROY. SOC. EDIN., VOL. LII, PART III (NO. 24) 
