30 STIGMARIA FICOIDES. 



of primary orientation, /', as in the three preceding smaller figures. In fig. 59 we 

 see at f" two vessels somewhat detached from the next one, /", and more deeply 

 embedded amongst the cells of the investing cylinder than is usual ; nevertheless, 

 these three linearly arranged Tracheids, along with those at /' constitute the 

 monarch point, to which the remaining vessels of the bundle were added centri- 

 petally. In figs. 60 and 61 a further increase in the same direction is seen. 

 There are about sixty-four vessels in fig. 60 and seventy-five in fig. 61 ; the 

 apparent adhesion of the left-hand side of the bundle to the bundle sheath in 

 fig. 60 is merely accidental, not organic. The only material changes to be noted 

 are that the section of the latter bundle has become increasingly wedge shaped, 

 and the newer Tracheids, /", are more obviously arranged in radiating series 

 than are the older ones,/", changes which are yet more conspicuous in fig. 60. 

 It is important to note that every intermediate condition exists between the 

 pyriform bundles of figs. 57 and 58 and the wedge-shaped bundles of figs. 60 and 61, 

 since M. Renault has attempted to show that these extreme modifications of a 

 graduated series represent important morphological and functional distinctions ; 

 a subject to be discussed immediately. Equally important is the fact that each 

 bundle commences its growth from a single point,/', not at three points, as is 

 affirmed by M. Renault ; nor yet at two semi-contiguous points, which become one 

 by coalescence, as M. van Tieghem believes to be the case with the representative 

 bundles in the roots of living Lycopods. 1 



We now know that on its primary appearance in any young root, the vascular 

 xylem almost invariably takes the shape of two or more groups of minute vessels, 

 symmetrically arranged round the periphery of a central cylindrical strand of 

 small meristematic cells. Sachs has designated this axial strand a procambium, 

 Nageli a cambium strand, Russow a desmogen, and De Bary an axial meriste- 

 matic or initial strand of a vascular bundle. Tbe number of initial vascular points 

 varies much. But the number is conveniently designated by the terms monarch, 

 diarch, triarch, &c, whatever that number may be. The peculiarity of these 

 initial vascular points is that additions are made to them centripetally, until, in 

 many cases, these additional growths meet in the centre of the young root, 

 occupying, more or less completely, the medullary area. The name of xylem 

 plates is given to these vascular growths. Midway between these several initial 

 points, or points of orientation, we find small patches of phloem. 



This question only concerns us now so far as it affects our study of the 

 Stigmarian rootlets, which it does very materially, because of distinct peculiarities 



1 Of late years tbe primary structure and ultimate development of roots has attracted a large 

 amount of attention amongst the most distinguished European botanists. An important memoir by 

 M. van Tieghem (" Recherches sur la symetrie de structure dans les plantes vasculaires. ' Annales 

 des Sciences natureiles,' 5me serie, tome xiii) has done much to stimulate further inquiry into the 

 subject. 



