50 Principles of Plant Culture. 
lets. In the roots, they divide in a similar manner, extend- 
ing lengthwise through all the branches and branchlets. 
Fig. 20 shows a cross section of a vascular bundle of the 
sunflower. 
Fic. 19. Showing cross section of a vascular bundle of the common sunflower, 
(Helianthus annuus). Highly magnified. (After Prantl). See also Fig. 20. 
The threads in the stalk of Indian corn and the leaf stem 
of the plantain (Plantago) furnish examples of well-defined 
vascular bundles. In most stems, the vascular bundles are 
less clearly defined. In woody stems, they are closely 
crowded, which gives the wood its firm texture. In some 
woody plants, as the grape and the elder, a cylinder extending 
through the center of the stem is free from vascular bundles, 
forming the pith. The young stems of asparagus, the ball 
of the kohl-rabi and the roots of turnip become “stringy ” 
when the cells of their vascular bundles become thickened 
by the deposit of woody material in them. 
69. The Cambium (cam’-bi-um) Layer. In most 
plants having two or more cotyledons (46), a layer of cells 
that are in a state of division (15) exists between the bark 
and the wood, called the cambium or cambium layer (Fig. 20). 
