35.] 



CHAPTER II. THE TISSUES. 



195 



but occasionally, especially in soft wood, the walls are reticulately 

 thickened. 



The secondary wood-parenchyma consists of oblong cells, which 

 are generally so arranged that their long axes are parallel to that 

 of the member of which they form part : they occur in short 

 longitudinal strands, consisting commonly of a single row of cells 

 (Fig. 148(7), but sometimes, in the middle only, of more than one 



FIG. 147. Transverse section of a root of the Yew (Taxus baccata) which has begun to 

 grow in thickness: c cortex; m sub-endodermal layer (see p. 166); e endodermis; p peri- 

 cycle ; s protoxylem-group of one of the two confluent primary xylem-bundles ; t' tracheids 

 of primary wood ; / interfascicular conjunctive tissue ; t" secondary wood formed from a 

 cambium-layer situated just externally to it ; v' 1 secondai'y bast ; v' primary bast which 

 is becoming crushed and disorganised by the cambial development of new tissues ; fc cells 

 of secondary bast, containing crystals ; r cells of pericycle containing resin. (After Stras- 

 burger ; x 42). 



row. They are true cells, containing protoplasm and a nucleus, 

 and other substances, such as starch (especially in perennial stems 

 and roots in winter), tannin, etc. Their walls are generally 

 lignified, but usually not very much thickened, and have circular 

 or elliptical simple pits. In many soft fleshy stems and roots 

 (e.g. Potato, Radish, Turnip, Beetroot), where this tissue is the 



