508 Bailey and Thompson.—Additional Notes upon the 
tracheides in injured roots and first annual rings of stems of Drimys ? 
Obviously, these traumatically produced elements might logically be con¬ 
sidered to indicate that the ancestors of the existing species of Drimys 
possessed tracheides with scalariform bordered pits, such as occur in the 
normal secondary xylem of Tetracentron and Trochode 7 idron (PI. XVI, 
Fig. 6), and were present in that of a number of Mesozoic and Palaeozoic 
plants (Fig. n). 
However, it was appreciated by Jeffrey and Cole that their interpreta¬ 
tion of the phenomena in injured roots of Drimys —as traumatic recapitula¬ 
tions of ancestral structures in a very c conservative ’ organ—would lose much 
of its significance if scalariform elements occurred in the secondary xylem of 
stems and in uninjured roots. Therefore, much emphasis was placed upon 
the fact that scalariform tracheary pitting does not occur in stems and un¬ 
injured roots except in the immediate vicinity of the primary xylem. 
Recently the writers have examined a considerable amount of material 
of various species of Drimys . This material included stems and roots of 
plants grown in their native habitats in South America and Australasia, and 
plants grown in nurseries and greenhouses in England and the United 
States. As is shown in Plate XVI, the tracheides were found to vary 
considerably in size and in the thickness of their secondary walls. In 
certain specimens (Figs, i and 5), growth layers or concentric rings were 
clearly differentiated; whereas in others there were only slight indications 
of zonation (Figs. 2, 3, and 4). In the stems of D. Winteri , Forst., secured 
from small plants grown in greenhouses, and in stems of D. colorata , 
Raoul, and D. axillaris , P'orst., from New Zealand, the tracheides were 
provided with one or two rows of circular bordered pits in their radial 
facets (Text-fig. 4, and PI. XVI, Fig. 8). On the other hand, in stems of 
D. Winteri from Chile and in roots of D. colorata and D. axillaris from New 
Zealand, the larger tracheides tended to have several rows of bordered pits 
in their radial walls (Text-fig. 3, and PI. XVI, Fig. 7). Scalariform pits were 
of more or less frequent occurrence in many of these tracheides (PL XVI, 
Fig. 12). They occurred in normal uninjured stems and roots, and in the 
later as well as the earlier formed portions of the xylem. In young stems 
—showing 5-15 growth layers—of D. Winteri from South America, the 
secondary xylem not infrequently resembled that which occurs in Tetra¬ 
centron. Growth layers were clearly differentiated (PI. XVI, Fig. 5). The 
larger, first-formed tracheides in these concentric rings were typical scalari¬ 
form, whereas the smaller terminal tracheides possessed circular bordered 
pits (PL XVI, Fig. 10). Transitional types of pitting occurred in interme¬ 
diate tracheides. In other words, the layers of scalariform tracheides, 
as in Tetracentron , were separated by zones of non-scalariform tracheary 
elements. 
It is evident, accordingly, that scalariform pits may occur in the normal 
