144 



BOTANY 



PAIIT I 



FIG. 167. Transverse section of a stem of Ansto 

 lochia Sipho 5 mm. in thickness, m, Medulla 



INTERFASCICULAR CAMBIUM connects the FASCICULAR CAMBIUM within 



the bundles, forming a complete hollow cylinder of meristematic tissue. 



The cells grow in the radial 

 direction and undergo division 

 by tangential and by transverse 

 walls ; from time to time cells 

 appear to be divided by radial 

 walls. 



Figs. 167 and 168 represent the 

 formation of the cambium as shown 

 particularly clearly and simply in a 

 transverse section of the stem of 

 Aristolochia Sipho. A single bundle 

 with the adjacent interfascicular cam- 

 bium from the stem in Fig. 167 is 

 more highly magnified in Fig. 168. 

 The cambium is actively dividing, 

 and two partially-developed secondary 



fv, vascular bundle ; vl, xylem ; cb, phloem ; fc, vessels are seen at m". The outline of 

 fascicular cambium; ifc, interfascicular cam- the parenchymatous cells of the medul- 

 bium; p, phloem parenchyma; pc, pericycle ; j wMch ye Qri in to the 



sk, ring of sclerenchyma ; e, starch-sheath; c, . - . , , . ... , 



primary cortex; d, collenchyma in primary interfascicular cambium., can still be 

 cortex, (x 9. After STRASBURGER.) recognised. 



The cambium cells fit together without intercellular spaces and 

 form radial rows. They have the shape of elongated prisms more 

 or less flattened tangentially and with both ends pointed ; thus 

 the form of the cell appears very different in tangential, radial, or 

 transverse section (Fig. 169). The tangential walls, which form the 

 polygonal or rhombic main faces of the prismatic cell, are thin ; the 

 radial walls, on the other hand, are fairly thick and frequently pitted. 

 A middle layer of cells in the cambial zone forms the INITIAL LAYER. 

 Its cells remain permanently in the meristematic condition. They grow 

 in the radial direction, dividing by tangential walls, and so give off 

 daughter cells (tissue mother cells) to both sides, but more abundantly 

 on the inner side. These daughter cells in their turn may undergo 

 tangential divisions, . and, often after growing greatly in length and 

 breadth (Fig. 174) and changing their shape, become gradually trans- 

 formed into permanent cells of the secondary tissues. 



The cambium in giving off cells inwards must itself, as the stem grows in 

 thickness, be carried gradually outwards. The circumference of the cambial ring 

 must therefore be increased. This can only be effected by growth and increase in 

 number of the cells in a tangential direction. In transverse sections it appears as 

 if this came about by radial division of some of the cells. KLINKEN ( 78 ) has, 

 however, shown in Taxus that such divisions do not occur ; the number of cells in 

 the tangential direction is increased by an initial cell of the cambium dividing 

 transversely, and the ends of the two resulting cells becoming placed side by side 

 tangentially by sliding growth. 



