264 dc Fraine . — The Morphology and Anatomy of the 
rosette (Text-fig. 13, a). In this way the richly branched cushion of the 
adult becomes formed so that the final condition is an aggregate of 
closely approximating rosettes. The richly branched crown serves as a 
trap for sand and silt in which it becomes completely embedded. As 
the plant increases in size and vigour it will be noticed that from the 
centre of some of the rosettes more than a single scape is produced. 
Sometimes this appears to be the result of forking of the scape from its 
extreme base, but more usually is due to the precocious development of 
one or sometimes two axillary buds of the terminal leaves (Text-fig. 13, b). 
In these circumstances, if no additional axillary buds develop, the life of 
the branch ends with the withering of its leaves. The main stem is 
usually small in diameter, though in a good-sized Main bank plant it may 
reach as much as 1 cm. across. Text- 
14 , A, shows the arrangement of the 
various tissues in the stem of a tall 
form plant. The pith ( p.) is large, 
and composed of thin-walled paren- 
chyma, with practically no intercellular 
spaces ; numerous groups of sclereides 
{self varying very much in size, occur 
in it. Medullary rays {m.r.) of thin 
walled cells break up the vascular 
ring into numerous segmen t; the rays 
vary considerably in width, being often 
very broad where a leaf trace is making 
its exit. A group of sclereides is fre- 
quently found in the broad rays accom- 
panying the outgoing trace. 
The primary vascular strands are very numerous and of small size: 
secondary growth sets in early, and a narrow zone of secondary wood (xy.) 
composed of vessels embedded in fibrous tissue is produced ; annual rings 
cannot be distinguished in the stem as they can in the root. The ele- 
ments of the protoxylem have spiral markings, and the rest of the xylem 
is composed of vessels with simple pits on their walls. The secondary 
phloem is small in amount (pk.)> In the pericycle, masses of sclerenchyma 
fibres (sc.) occur opposite to each vascular wedge ; no endodermis can be 
distinguished. 
The cortex (co.) is made up of small celled, rounded parenchyma, 
with little intercellular space system ; very numerous groups of sclereides 
(set.) occur in it, their walls are strongly thickened, and they have many 
branched pits. A broad zone of periderm (per.) limits the stem. As in 
the root, he cells of the periderm and many of the thin-walled cortical cells 
have contents which are of the nature of tannin (cf. p. 359) ; this substance is 
Text-fig. i 3. Diagram of the longi- 
tudinal section through the apex of rosettes of 
S. binervosa. Explanation in text. 
