THE FUNDAMENTAL SYSTEM. 



125 



however, it usually includes several, or even many, layers of 

 cells, or the whole of each of the tissue-masses (e.g., colleu- 

 chyma, sclerenchynia, etc.) which immediately underlie the 

 epidermis (Fig. 110, g, i). 



The remaining portion of the fundamental system, inside 

 of the hypoderma, is designated by Sachs as the Intermediate 

 tissue. The term is of but little value in many of the higher 

 plants, where more particular names may be applied ; but in 

 some Monocotyledons, most Pteridophytes, and in Bryo- 

 phytes it is very 

 serviceable. 



156. Cork. 

 Within the zone 

 which the hypo- 

 derma includes 

 there frequently 

 takes place a pe- 

 culiar develop- 

 ment of the 

 young parenchy- 

 ma, giving rise 

 to layers of dead 

 cells, whose cav- 

 ities are filled 

 with air only. 

 The walls in 

 some cases (e.g., 



tlio r>rT-lr roV\ aro 

 tne COrK-OaKj aie 



thin and weak, 



while in others (e.g., the beech) they are much thickened, 

 and in all cases they are nearly impermeable to water. True 

 cork is destitute of intercellular spaces, its cells being of 

 regular shape (generally cuboidal) and fitted closely to each 

 other (Fig. 111). 



157. Cork substance is formed by the repeated subdivis- 

 ion of the cells of a meristem layer of the fundamental tissue 

 (Fig. Ill) ; these continue to grow and divide by parti- 

 tions parallel to the epidermis, forming layers of cork with 

 its cells disposed in radial rows (Fig. Ill, k). Shortly after 



Fig. 111. Transverse section of one-year old stem of Ai- 

 lant/itig glandulosm. e. epidermis ; *, cork-cells ; r, inner 

 green cells, the phelloderma ; between k itnd r a layer of 

 cells tilled with protoplasm, called the phellogen or cork 

 cambium. X 350. After Prantl. 



