STIGMARIA. 



271 



-.'' '-\V '!""' ' -i /' 



approximately quadratic transverse section, arranged in regular rows. But 

 just on the innermost margin of the wedge this regularity is lost, and the ele- 

 ments, which have a much smaller transverse section, are no longer arranged 

 in rows. Here too the secondary rays come to an end, being separated from 

 the inner margin of the wedge by a narrow tissue-layer, as is shown in 

 Williamson's figure 1 . In many, but by no means in all cases, a peculiar 

 disturbance of a different kind makes its appearance here and there in 

 the wood 2 , much narrower elements in much more numerous radial rows 

 being quite suddenly formed over larger or smaller segments of the 

 circumference. If this occurs on an extended scale and at one time, the 

 appearance may be that of the formation of an annual ring. If on 

 the contrary it is confined within narrower limits, then it looks as if 

 patches of a different character had been in- 

 troduced into the otherwise uniform ring of 

 wood. 



The traces of the appendages, which have 

 their origin on the inner margin of the wedges^ 

 traverse the broad rays which separate the 

 wedges, and pass out into the rind 3 . As their 

 course is at first ascending inside the ray, 

 then almost horizontal and curving outwards, 

 the transverse section meets them sometimes 

 in the transverse, sometimes in the longi- 

 tudinal or even in the. oblique direction. 

 Where they are cut through transversely, they always appear as long 

 narrow wedges which are composed of a few rows of tracheides lying 

 near one another and separated by rays. In certain circumstances they 

 might be taken for narrower intercalated segments of the woody ring. 

 Their appearance therefore favours the supposition that they partici- 

 pate in the further growth in thickness of the ring. Very instiuctive 

 pictures quite confirming this view are afforded by tangential sections, such 

 as those described and figured in Brongniart* and Williamson 5 (Fig. 33 A, B}. 

 Here the rays which separate the wedges appear as broad fissures much 

 elongated in the direction of the apex, of moderate depth, and often showing 

 at the margins traces of preserved parenchyma. But from the basal end 

 of every fissure of the kind there springs a broad cone-like process, the 

 elements of which are shown in longitudinal section below, in transverse 

 section at the apex. It is the section through the lowest extremity of the 

 leaf-trace, so far as its course is vertical. And as the same picture is obtained 

 in every tangential section, whether made outside or inside in the wood, it 



FIG. 32. Stigmaria ficoides. Transverse 

 section of the axis ; beneath is the rind 

 bearing the two appendages cut through 

 longitudinally. Above is the ring of wood 

 composed of numerous wedges. After 

 Williamson, reduced. 



1 Williamson (6), t. 4. 2 Williamson (6), t. 4 ; Gbppert (1), t. 13, f. 31. 3 Brongniart (7), 

 t. 29, f. 3. 4 Brongniart (7), t. 29, ff. 6, 7. 5 Williamson (6), t. 5. 



