HISTOLOGY AND PHYSIOLOGY. 



in size, fuse laterally into a continuous mass, the cambium 

 in each joining with that of the adjacent bundle, thus form- 

 ing a cambium zone, or layer, which annually produces a 

 ring of wood, as in forest trees. (See AngiospermcB, Part 

 III). Closed bundles do not increase in size, and plants 

 having such (as the Asparagus, etc.) do not form an annual 

 ring of growth. 



122. The fundamental tissue includes all except the 

 epidermal tissue and the fibro-vascular bundles. It con- 

 sists mainly of parenchyma of various forms, in contact 



with or near the epi- 

 dermis. CoUenchynia 

 is sometimes present. 

 This is replaced by 

 sclerenchyraa in parts 

 requiringgreater firm- 

 ness than that given 

 by the former. The 

 term hypoderm (Gr. 

 hypo, under ; dermd, 

 ekin) has been used to designate those difierentiated por- 

 tions lying immediately beneatb the epidermis (Fig. 202, 

 hy). Laticiferous vessels may also occur in the funda- 

 mental tissue. To this tissue belong the medullary 

 rays in woody plants. Within the zone of the hypoderm, 

 or immediately below the epidermis, layers of cork may 

 be developed (Fig. 216, C). The cells are generally four- 

 sided in section, filled with air, have thin walls, impermeable 

 to water. The generating tissue (Fig. 216, ph) is called 

 cork-cambium, or pheUogen (Gr. phellos, cork ; genein, 

 to be produced). When a plant is slightly cut or injured, 



Fig. 216, A la^er of cork-cells (C) forming the covering of the Potato. 



