78 PRACTICAL BOTANY 



sionally by radial walls. An interfascicular cambium 



is thus formed, and by the tissues derived from it the 

 vascular ring, as seen in the older stem, is completed. 

 Centrally lies 



4. The pith, consisting of thin-walled cells, with 

 sparing cell-contents : thus these cells have not yet lost 

 their activity : compare the older stem, where the pro- 

 toplasmic contents are replaced by air. 



Note on Interfascicular Cambium. It has been seen 

 that in the Sunflower the bundles are quite separate 



FIG. 4. A, B. Diagrams illustrating the formation of interfascicular cambium. 

 A shows the primary vascular bundles isolated, and embedded in quiescent 

 ground tissue, before the interfascicular cambium begins to be formed ; B shows 

 the interfascicular cambium (ic) forming with the fascicular cambium (fc) a 

 continuous ring: p = phloem; a; = xylem; b, b, groups of bast-fibres at the 

 periphery of the phloem. (After Sachs.) 



in the young stem, being isolated by masses of quiescent 

 ground tissue. Later, the cells of the latter tissue begin 

 to divide actively as an interfascicular cambium 

 layer, lying between the originally separate bundles. 

 This interfascicular cambium joins the margins of the 

 fascicular cambium, and a complete cambial cylinder 

 is thus formed. But here in the Sunflower, as in most 

 herbaceous annual plants, the interfascicular cambium 

 is not very long active, the product of its activity being 



