n8 



CAMBIUM 



Px 



coming differentiated as additional (secondary) phloem, those 

 adjacent to the xylem as additional (secondary) xylem. 



Subsequent to the development of the cambium within the 

 bundles a similar division by two parallel tangential walls takes 

 place in certain of the cells of the medullary rays, and, where a 



starch-sheath is 

 present, such 

 divisions will be 

 recognised as 

 occurring in the 

 pericyclic layer 

 (e.g. hypocotyl 

 of the Castor 

 Oil plant, Fig. 

 57, I.e.). In 

 this way a cam- 

 bium between 

 the bundles 

 (interfascicular, 

 Fig. 57, I.c.) 

 links up with 

 that within the 

 bundles (intra- 

 fascicular, Fig. 

 57, C.) to form 

 a complete cam- 

 bial ring. In 

 some plants, 

 however, the 

 formation of 

 inter- and intra- 

 fascicular cam- 

 bia takes place 



almost simultaneously. The subsequent division of the inter- 

 fascicular cambium is like that of the intrafascicular, so that 

 the whole cambial cylinder cuts off segments on both sides. 

 In woody perennials the cambium resumes its function each 

 year, although division is arrested during the winter months 

 (cf. below). 



Coll. 



FIG. 57. Transverse section of a small portion of 

 the hypocotyl of the Castor Oil plant (Ricinus 

 cotntnunis}. C., intrafascicular cambium ; Co., 

 cortex ; Coll., collenchyma ; F., pericyclic fibres ; 

 I.e., interfascicular cambium ; P., parenchyma ; 

 Ph., phloem ; Px., protoxylem ; S.s., starch 

 sheath. 



