182 ON THE STRUCTURE OF THE WOODY ZONE IN CALAMITE. 



into the interior of another rootlet which only happened 

 to be a size larger than itself. 



EXPLANATION OF PLATES I.-V. 



1. Specimen of Calamite from a Coal-measure Sandstone-Quarry near Old- 



ham : a, lower end of the pith, consisting of seven or eight joints ; 



b, two verticils of medullary prolongations, or " verticillate medullary 

 radii" penetrating the ligneous zone c ; d, single joint of a Calamite, 

 enclosing the above ; e, supposed bark, replaced by sandstone. 



2. Exterior of specimen of Calamite in ironstone, as it existed before being 



cut up into microscopic sections : a, internodes ; h, nodes ; c, pro- 

 jecting wedges of reticulated vessels ; d, intermediate tracts of fusi- 

 form cells, or prosenchyma ; /, extremities of " verticillate Tnedullary 

 radii''' 



3. Transverse section through the centre of an internode : «, pith ; c, c, 



two vascular laminae ; c' , c', inner margins of the same laminse, cor- 

 responding to longitudinal grooves of Calamite ; d, a prosenchy- 

 matous lamina. 



4. Transverse section of vessels of fig. 3 c, more highly magnified. 



5. Transverse section of prosenchymatous cells of 3 d, more highly magni- 



fied : a, proper cell-wall ; h, infiltrated mineral matter. 



6. Tangential section of part of a node, and of the internode below, made 



transversely to the verticillate medullary radii : c, c, two vascular 

 tracts ; d, d, d, portions of three prosenchymatous tracts ; d', con- 

 verging vessels near the base of a prosenchymatous lamina, supplying 

 a lateral branch above the node ; d", corresponding part to d^, but 

 not giving off a lateral branch ; /, /, /, three transversely divided 

 medullary radii. 



7. Portion of fig. 6 c, more highly magnified : e, e, medullary rays, divided 



at a right angle to their course ; g, g, elongated vessels. 



8. Portion of prosenchymatous tract, fig. 6 d, with the fusiform cells more 



highly magnified. 



9. Vertical section of a vascular tract, made in the plane of a medullary ray : 



c, reticulated vessels ; e, cells of a medullary ray in their lateral 

 aspect. 



10. Vertical oblique section of a node, nearly in the plane of one of the 



medullary radii : a, pith ; b, central internal projection of the node 

 into the pith ; c, vascular tract above the node ; d, prosenchymatous 

 tract below the node ; /, medullary radius. 



11. Transverse section of part of fig. 10 c, nearly in the plane of b, con- 



sisting of transversely divided vessels disposed in radiating lines : 

 i, i, small groups of irregular prosenchymatous cells at each inner 

 angle of the projection. 



12. Two vessels of fig. 9 c, more highly magnified. 



