1054 
de Fraine . — On the Sir uc tur e and 
tracheides of the more or less concentric strands owing to the crushing 
which has usually taken place. 
Scattered throughout the series in the band of tissue immediately 
beyond the secondary phloem of the ‘ meristeles 5 (probably the pericycle) 
are found clusters of isodiametric tracheides with reticulate markings 
exactly resembling those which occur on the inner margin of the wood 
of the extrafascicular strands (PL XCI, Fig. 5). It is suggested that these 
strands of short tracheides may have been directly derived from the 
delicate parenchyma cells of the inner cortex to facilitate the storage of 
water. Strands or clusters of storage tracheides once having been formed 
may possibly have provided a starting-point or ‘ nucleus ’ around which 
cambial activity being initiated secondary formation of xylem and phloem 
began ; the ultimate product of the secondary growth being the diversely 
organized extrafascicular arcs which form so characteristic a feature of the 
fossil. It may perhaps be pointed out here, though the question wall 
be discussed later, that these strands are regarded as entirely secondary 
structures and are not considered to have any phylogenetic connexion with 
the stele or f meristeles ’. 
The short tracheides at once recalled the somewhat similar, pitted, 
isodiametric tracheides described by Seward 1 in Megaloxylon, but in that 
genus they compose the bulk of the primary wood, and they certainly have 
no connexion with that tissue in Sutcliffia. The occurrence of parenchyma- 
tous tracheides, reticulately marked but with scattered bordered pits, has 
been described by Rothert 2 as present singly or in groups in species of 
Cephalotaxus where they represent modified elements of the pith. As 
in the case of Megaloxylon , the function of water storage is assigned to them, 
and a comparison is instituted with the similar cells found in Nepenthes , 
Salicornia sp., Crinum , and certain members of the Orchidaceae. Thus the 
conversion of parenchymatous cells into short tracheides for the purpose of 
water storage appears to be a not uncommon phenomenon. 
In this connexion it may be noted that Lang 3 observed the occurrence 
of short tracheides in a species of Ophioglossum ; they were mixed with the 
parenchyma of the pith and f apparently derived by the conversion of some 
of the medullary cells into tracheides ’. A similar phenomenon may occur 
in Botrychium. Lang notes, however, that in both cases the stimulus to 
the development of the tracheides may have been traumatic. 
The fact of the greatest interest in connexion with these extrafascicular 
1 Seward, A. C. : Notes on the Binney Collection of Coal-Measure Plants. Part II, Mega- 
loxylon , gen. nov. Proc. Camb. Phil. Soc., vol. x, Part III, 1899. 
2 Rothert, W. : Uber parenchymatische Tracheiden and Harzgange im Mark von Cephalotaxus- 
Arten. Sonder-Abdruck aus den Berichten der Deutsch. Bot. Gesellsch., Jahrgang 1899, Bd. xvii. 
3 Lang, W. H. : On the Interpretation of the Vascular Anatomy of the Ophioglossaceae. 
Mem. and Proc. of the Manchester Lit. and Phil. Soc., vol. lvi, Part II, 1912. 
