Comparative Anatomy of the Casuarineae. 245 
In some species this type of vessel clearly predominates 
(Figs. 19, 25). In others, however, the single perforation is, 
in the majority of elements, replaced by a large number, often 
as many as twelve, of ladder- or slit-like perforations, which 
give a very characteristic appearance to these elements ; in 
these cases the round or oval form of the wall remains 
unchanged. In such a stem as, e.g., that of a doubtfully- 
named species which we examined, one may find all tran- 
sitions from these ladder-like perforations to the single, 
round perforation above-mentioned ; from the complex net- 
work shown in one vessel in the plant mentioned, and figured 
in the drawing, the transverse bars gradually become fewer 
and fewer in number and the perforations between them 
correspondingly wider, till, as seen in some elements, only 
three, two, or even one flimsy bar stretches across, or only 
part way across, the perforation (Figs. 20-22). 
In many cases tertiary spirals occur in the vessels ; these 
are often very conspicuous, and sometimes double. 
In the primary wood, however, we get, as it were, quite 
a different series of vessels, though many of the forms found 
here also occur here and there in the secondary wood. In 
one instance, shown in C. muricata , Roxb., quite near the 
protoxylem, were some very narrow elements with extremely 
oblique terminal walls, on which was a row of small, irregularly- 
shaped perforations, precisely identical with those to be 
described and figured later on for Carpinus. Another case 
showed a narrow vessel with three small , round perforations, 
placed at short distances from one another on a very oblique 
terminal wall. As showing what would appear as the result 
of the fusion of the several perforations in the two latter cases, 
elements frequently occurred, usually slightly further on the 
outside, with a single, long, narrow perforation, at whose 
edges slight projections were seen, indicating where the trans- 
verse bars in an earlier formed element would have stretched 
across. Fig. 18 also shows a case of an element from the 
primary wood. One more case worth mentioning, as forming 
a connecting link with the tracheides, was that of a terminal 
