XXX] SUTCLIFFIA 151 



anglica except in the possession of exarch protoxylem strands. 

 The metaxylem tracheids contiguous to the external protoxylem 

 elements have a dense spiral or scalariform type of pitting. In 

 the lower part of the stem the primary xylem is enclosed by a 

 cambium which has added a few secondary tracheids (120/t in 

 diameter), but in the upper part of the specimen the cambium is 

 only partially developed and the addition of secondary xylem has 

 hardly begun (fig. 440). A narrow band of secondary phloem 

 was recognised in places consisting of small-celled parenchyma 

 with some sieve-tubes and medullary rays continuous internally 



FIG. 440. Sutcliffia insignis. Part of the primary xylem showing on the upper 

 edge the beginning of secondary growth. (Cambridge Botany School, 560.) 



with the parenchyma of the primary stele. In close association 

 and occasionally in organic connexion with the surface of the 

 stele are several tangentially elongated and large groups of vascular 

 tissue associated with smaller oval strands varying considerably 

 in size. These groups, designated meristeles (Fig. 439, A), are 

 identical in structure with the main stele and are occasionally 

 invested by a feebly developed zone of secondary xylem and 

 phloem. The meristeles are detached at intervals from the parent 

 stele around which they form by anastomoses an irregular network : 

 the larger meristeles give off smaller strands and from these the 



