5 io Boodle. — On the Occurrence of 
blue or green walls in the first preparation showed full coloration with 
phloroglucin in the other. 
Fig. 3, PL XXXIII, is a section cut at the point marked c in Fig. 44 
in the text. It shows a conspicuous band of primary tracheides and a large 
number of smaller secondary tracheides, among which one group of four, 
marked ^ in this figure, is drawn further enlarged in Text-Fig. 50. The 
three elements with the darker walls are incompletely lignified. 
Fig. 4, 5, and 6 in PI. XXXIII are transverse sections of the stock of the 
aerial branch e in Text-Fig. 44, cut at three levels in ascending order. Their 
positions are indicated by letters : a is the level of Fig. 4, b that of Fig. 6, 
and about half-way between a and b is the position of Fig. 5. In these 
three sections numerous secondary tracheides are present, many of them 
being incompletely lignified. In Fig. 4 the primary xylem can be re- 
cognized as a broad plate of tracheides. In Fig. 5 the xylem has become 
roughly triangular, and at r a parenchymatous ray is seen running inwards 
as far as one of the protoxylem-groups, in which there is a crushed 
tracheide. In Fig. 6 the primary xylem-group is considerably larger than 
in Fig. 5, triangular and doubtless triarch. At several points outside the 
primary xylem, e. g. at r, radial arrangement is found among the parenchyma 
and secondary tracheides. 
Fig. 49 in the text is from a transverse section through the lower part 
of an aerial shoot. It shows some primary tracheides (< a ), and two secondary 
tracheides (b, b). The latter are incompletely lignified, and still contain 
a protoplasmic lining. Similar cases were met with in many of the sections. 
The nature of the secondary tracheides may now be referred to. They 
are scalariform, or sometimes rather irregularly pitted, and they frequently 
have a sinuous course, while the primary tracheides are generally straight. 
This must be due to their having to push their way among mature paren- 
chyma, &c., by sliding growth. Fig. 47 in the text shows a secondary tracheide 
with a constricted part, probably owing to some of the adjacent elements 
having resisted compression more than others. The secondary tracheides 
frequently occur in groups similar to that seen at 5 in Fig. 3, PL XXXIII, 
and often one or two of the parenchymatous cells immediately adjoining 
such groups have become partially or completely collapsed L Fig. 48 in the 
text is a scalariform secondary tracheide showing its sinuous course. 
From the material examined it cannot be definitely stated how high 
up in the aerial stem secondary tracheides may occur, but in one specimen 
several were present in a stele containing a fair-sized central group of 
sclerenchyma. 
The examples of the occurrence of secondary tracheides chosen for 
illustration in PL XXXIII do not include any case in which it was perfectly 
clear that the organ in which they were present should be classed as 
1 The rigidity of the cortex preventing expansion of the stele. 
