132 



BOTANY 



In the bast strands of Gymnosperms, the phloem elements produced 

 by the cambium (Fig. 140, c) consist solely of sieve-tubes, the paren- 

 chymatous cells of the bast parenchyma (p and h), and, in certain cases, 

 of bast fibres. These elements of the bast generally form alternating 

 bands. 



In the Pine and other related Abietineae the bands of sieve -tubes are in- 

 terrupted only by bands of bast parenchyma containing starch (Fig. 140, p), and 





Fig. 147. — A radial section of the wood 

 of Tilm parvifolia, showing a small 

 medullary ray. g, Vessel ; I, wood 

 fibres; tra, medullary ray cells in 

 communication with the water-courses 

 by means of pits ; sm, conducting cells 

 of the medullary ray. (x240.) 



in> p 



Fig. 148.— Tangential section of the wood 

 of Tilia parvifolia. m, Pitted vessel ; 

 1, spiral tracheids ; p, wood paren- 

 chyma; I, wood fibres; r, medullary 

 , rays, (x 160.) 



also tannin-like substances and crystals (k) deposited in single, vertical rows of 

 cells. Other Conifers, the Araucaricae, Taxineac, and some of the Oupressineae 

 exhibit definite, vertical rows of bast parenchyma cells which are characterised by 

 their abundant albuminous contents. These cells stand in close relation to the 

 sieve-tubes and take the place of companion cells, which are not found in Gymno- 

 sperms. In the bast of the Taxineae, Oupressineae, and other nearly related 

 families there also occur tangential bands of strongly thickened bast fibres 

 which alternate regularly with tangential bands of sieve - tubes and bast 

 parenchyma. 



