138 



BOTANY 



I'AUT I 



sieve-tubes ; storage and conduction of carbohydrates take place in 

 the parenchyma in which bye-products of metabolism, such as tannins 

 and calcium oxalate, also accumulate. 



As in the case of the wood, the elements of the bast may be referred to two 

 forms of tissue, the sieve-tube and the parenchymatous. The former is represented 

 by the sieve-tubes or by these together with companion cells, the parenchymatous 

 portion by the phloem parenchyma and the bast fibres, between which there are 

 intermediate forms of element. 



In the bast strands of Gymnosperms, the phloem elements pro- 

 duced by the cambium (Fig. 141 ft, c) consist solely of sieve-tubes, 



-.". 



;'// tm 



fZfe.~-*J 



; .T 

 - - 



-pm 



FIG. 146. Transverse section of a stem of Tilin 



in the fourth year of its growth. 

 pr, Primary cortex ; c, cambium ring ; cr, bast ; 

 pm, primary medullary ray; pm', expanded ex- 

 tremity of a primary medullary ray ; am, second- 

 ary medullary ray ; g, limit of third year's wood. 

 (x 6.) 



KM.. 147.- A radial section of the wool of 

 Tiliii ulmijuliii, showing a small medul- 

 lary ray. g, Vessel ; I, wood fibres ; ////. 

 medullary ray cells in communication 

 with the water -courses by means of 

 pits ; snt, conducting cells of the medul- 

 lary ray. (x '240.) 



the parenchymatous cells of the bast parenchyma (p and /,), and, in 

 certain cases, of bast fibres. These elements of the bast generally 

 form alternating bands. 



The Araucarieae, Taxineae, and Cupressineae have definite, vertical rows of 

 bast parenchyma cells which take the place of the companion cells wanting in 

 these plants. At a certain distance from the cambium the sieve-plates become 

 overlaid by callus. During the vegetative period following their development, 

 the sieve-tubes become empty and compressed together (Fig. 141 B, cv). The 

 rows of bast parenchyma cells containing albuminous substances, which are 

 found in some Conifers, undergo disorganisation at the same time as the adjacent 

 sieve-tubes ; the bast parenchyma cells which contain starch, on the other hand, 

 continue living for years, and even increase in size, while the sieve-tubes become 

 compressed. 



The elements of the phloem tissue included in the bast strands 



