Cooke. — Observation* on Salicornia australis. 



359 



to elongation. There are numerous pits, simple, both in radial and oblique 

 walls. 



As the cells always remain living, there is no differentiation into heart 

 and sap wood. 



No sclerenchymatous fibres were found anywhere. 



Medullary Rays. — Primary medullary rays are not continued through 

 the secondary wood, and, as a rule, no clearly distinguished secondarv 

 medullary rays are formed ; nor is there any necessity for them, seeing that 

 most of the xylem-cells are living and are connected by pits. Occasionally- 

 1 found a distinct medullary ray, the cells of which were elongated radially, 

 being three times as long as they were broad, and narrower than the fibrous 

 cells. There occur also a number of bands of cells one or two wide, the 

 cells having then radial diameters slightly longer than the tangential. 

 These resemble the medullary rays in Mahonia given by Schleiden, where 

 they are very thick-walled, and scarcely to be distinguished from the 

 fibrous cells of the wood. In Salicornia they are packed with starch-grains. 



The result of this slight development of medullary rays is that they are 

 not observable in longitudinal section. 



Cork ceils ? V^ U ° S ^,' c Uod crr ' 1 



Phloem? 



6-. C Xylen-,2 



Fibrous 

 cells Tracheal 



Phloem island 



Fig. 8. — a, Longitudinal section of stem of secondary growth; 6, pits in trachea; 

 r, longitudinal section showing periderm. 



A cross-section of a branch which has remained succulent all the winter 

 shows not only the fascicular cambium dividing and increasing in size, but 

 cells are dividing between the bundles to form interfascicular cambium 

 (fig. 7). When the bundles are close to each other the dividing cells reach 

 right across, but when far apart the line of the dividing cells curves out- 

 wards and joins on to the extra -fasicular cambium, forming a complete ring 

 round the phloem. 



The interfasicular cambium does not long remain functional, and the 

 majority of secondary tissues are formed from the extra-fascicular cambium 

 as usual. 



The Formation of Cork.— As winter advances, as a rule, all the branches 

 formed in spring assume a different appearance. The succulent tissue 

 becomes withered and turns brown, the free portion of the leaves of each 

 internode surrounding the base of the internode above like a collar. This 



