64 PRACTICAL BOTANY. 



tissue. In slightly older stems the cells of this tissue 

 may be found actively dividing, by tangential and 

 occasionally 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. These, then, have not yet lost 

 their cell-nature ; compare the older stem where the 

 protoplasmic contents are replaced by air. 



Note on Interfascicular Canibium. We have seen 

 that in the Sunflower the bundles are quite separate 

 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 cam- 

 bium 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 but a narrow band of secondary fascicular 

 tissue : the identity of the original bundles can thus be 

 recognised at a glance. In some stems (Ranunculaceai) 

 the interfascicular cambium is completely absent. 



Compare this with the case of most ligneous perennial 

 plants, e.g. Elm, Pine. 



Apical Bud. 



V. Take the apical bud of a young plant, or of a 

 young lateral branch of the Sunflower, and cut longi- 

 tudinal median sections : treat with potash, and mount 



