Cooke. — Observations on Salicornia australis. 



357 



A cross-section of a branch six months old shows just outside the phloem 

 a layer of cells divided usually by tangential and occasionally by radial 

 walls. Thus a complete extra-fascicular cambium ring is formed (see fig. 6). 

 This has been recorded by De Bary for Salicornia herbacea (1, e). The 

 xylem formed from this cambium consists of thick-walled fibrous cells, 

 among which are situated, in irregular rings, the vessels, with very large 

 lumens. The phloem consists of thin-walled cells, forming, as usual, a 

 cylinder outside the cambium. No sieve-tubes could be detected among 

 these cells, which in Salicornia amtralis always contain chlorophyll, and 

 are densely packed with starch-grains. Some of these cells disintegrate, 

 those remaining being arranged in radial rows, between which are large 

 intercellular spaces. 



Endodenhjs 

 \Pericycle 



\Cork cells 



Phellogen 

 ^7=fe^* — Pkelhderm 



^^ *> Phloem 2 



t. cambium 

 Phloem island 



Medulla 



Fig. 6. — -Transverse section of stem, showing extra-fascicular cambium ring 



(E. cambium). 



In addition to the phloem cylinder, there are phloem islands scattered 

 about in the fibrous cells of the xylem, in each case lying just outside the 

 large vessels, from which they are separated by only a few fibrous cells. 



A theory which might account for these phloem islands is this : The 

 formation of the large vessels consumes time ; while these are forming, 

 the cells each side of the group of vessels, growing more quickly, grow over, 

 enclosing a small patch of cambium. This gives rise to the phloem and 

 several small fibrous cells, the latter separating the phloem from the vessels. 



The phloem islands consist of thin-walled cells, which show great 

 uniformity in length. When stained with saffranin they are easily 

 distinguished, since they turn an orange colour, the cells of the xylem 



