ANATOMY 



461 



the stem of the young plant, but fades off in the upper regions, as in 

 Ophioglossitm. 



In transverse sections of the stock of Botrychium^ in which the leaf- 

 gaps are limited in area and not so closely placed as in Ophioglossum, 

 the vascular ring is often seen to be complete, or where a leaf-trace issues 

 it may be interrupted : the xylem is endarch. Much importance has 

 been accorded to the secondary thickening seen in both stem and root 

 of Boirvchium. A sluggish cambium appears between the phloem and 

 xylem, and may even be seen to be active close below the apex before 

 either of those tissues are differentiated : it adds fresh tracheides to the 

 xylem, but little or nothing to the phloem, while the radially seriated wood 



A B 



Fit;. 258. 



Ophioglossum Bergiamon, Schlecht. A = transverse section ot the stock, showing a 

 large semilunar stele, with wide foliar .uap into which a small leaf-trace strand is entering. 

 .5=another section, showing probably the result of overlapping of the foliar gaps. X 200. 



is traversed by parenchymatous rays. The secondary activity extends also 

 into the basal region of the root, but it does not extend far along it. In 

 Ophioglossum the transverse section of the stock shows an interrupted 

 ring of xylem-bands, the interruptions representing the closely grouped 

 and overlapping leaf-gaps, as will be readily understood by comparison 

 of Fig. 236, Nos. 4, 5. But in simple cases, and especially near to the 

 base of the stock, the ring may appear more complete (Fig. 258). The 

 development is endarch, and there is no process of secondary thickening 

 except that a few tracheides may occasionally be added peripherally to 

 those primarily formed. In the root also there may be a feeble formation 

 of secondary wood, especially in the neighbourhood of the insertion of 

 an adventitious bud (Boodle). In Helminthostachys the vascular ring is 

 interrupted only on the oblique upper side, by the leaf-gaps. The xylem 

 is, however, mesarch, while the secondary thickening is altogether absent 

 (Farmer and Freeman). 



