506 Bailey and Thompson.-—Additional Notes upon the 
or scalariform bordered pits occurred in the lateral walls of the tracheary 
structures in the injured roots of Drimys. 
‘We may ask if the peculiar scalariform elements 1 occurring in the 
root of Drimys after injury are in reality to be interpreted as of the nature 
of vessels. They are certainly not to be considered as tracheides, since the 
sculpture of their walls is quite unlike that found in tracheides in general, 
and entirely resembles that observed as characteristic of vessels in the 
Magnoliaceae and other families.’ 
However, this conclusion does not appear to be substantiated by well- 
known facts in the anatomy of the higher plants, since tracheides with 
scalariform bordered pits occur in many Angiospermae, Gymnospermae, and 
Pteridophyta. 2 Even in secondary xylems, such tracheides are abundantly 
developed in certain representatives of the Calamariales, Sphenophyllales, 
Cycadofilices, and Bennettitales (PL XVI, Fig. n). 
In addition, it is to be emphasized that scalariform bordered pits are no 
more characteristic of the lateral walls of the vessels in the Ranales and 
other groups of the Dicotyledons than are ‘ multiseriate ’ circular types 
(Text-figs. 8 and 9). It is evident, accordingly, that the presence of non- 
perforate, scalariform bordered pits cannot be used as a reliable diagnostic 
criterion for distinguishing vessel-segments. 
If the scalariform elements that occur in the roots of Drimys are to be 
considered (phylogenetically) as members of vestigial vessels, it must be 
admitted that they have lost all the structural peculiarities of vessel-seg¬ 
ments and have reverted to typical tracheides. There is no direct evidence 
in favour of this hypothesis. Nor does the evidence that may be derived 
from analogy with other Dicotyledons appear to support this view. 
As has been noted by Eichler (1), Groppler ( 3 ), Harms ( 4 ), Solereder 
( 9 ), Van Tieghem ( 12 ), the writers ( 11 ), and others, the normal secondary 
xylem of Tetracentron and Trochodendron is characterized by the presence 
of tracheides with scalariform bordered pits (Text-fig. 1, and PI. XVI, Fig. 6). 
Although, upon the basis of Jeffrey and Cole’s hypothesis, these forms must 
be considered to be less ‘ degenerate ’ than Drimys , their scalariform 
elements are typical tracheides and no more resemble the segments of true 
vessels than do those which occur in injured roots of Drimys (Text-fig. 2, 
and PI. XVI, Fig. 9). Therefore Jeffrey and Cole’s argument, that ‘the 
general phenomenon of traumatism lead us to expect, more often than not, 
the recall of ancestral characters in an abnormal form ’, loses much of its 
significance. 
Although evidences of the partial or nearly complete suppression of 
vessels occur in a number of Dicotyledons, they occur usually in unusual 
growth forms, such as aquatics, much reduced parasites, extreme xero- 
1 Referring to elements of the secondary xylem with closed scalariform bordered pits. 
2 The terminology of Engler and Gilg is used in this paper. 
