RESIN PASSAGES. 143 



are sieve-tubes; corresponding to the places where, in the wood, 

 bordered pits stand, sieve-pits (e) will be found ; in very delicate 

 sections we can recognise the fine pores which traverse these sieve- 

 pits. Companion-cells are not developed to accompany the sieve- 

 tubes of Gymnosperms. Unilamellar bands of bast parenchyma 

 alternate with the thicker layers of sieve-tubes. They are in the 

 main composed of starch-containing cells, which in the older bast 

 swell considerably. Between the starch-containing cells, crystallo- 

 genous cells are scattered, which are very early marked by their 

 brown colour (k in Figs. 51 and 52). Only a proportionately 

 thin zone of the bast is composed of turgescent elements re- 

 taining their original order ; on the outer side of this zone the 

 radial rows become crumpled (see Fig. 51 cv, ante), the cell-walls 

 begin to turn brown, the cell-cavities are more or less crushed. 

 Only the starch-containing cells of the bast and the medullary ray 

 cells enlarge to any extent ; these become rounded, and appear 

 now as more or less spherical elements, densely filled with starch. 

 Ultimately the sieve-tubes and crystallogenous cells are quite 

 crushed, become tangentially stretched, and separate, in the form 

 of lamellae, the successive layers of large starch-containing cells. 

 The outer part of the bast appears, therefore, to consist of these 

 last alone. Externally we note thin layers of cork, and the deep 

 brown dead tissues, the Bark, which these have peripherally cut 

 off. 



Resin Passages. Thus far w r e have left unnoted the patches 

 of wood parenchyma which every cross-section of the wood shows, 

 and which always enclose a resin passage or resin canal (Fig. 

 53). In alcohol preparations this canal will have lost its resin 

 contents. The cross-section of the wood cuts the resin canals 

 also in cross-section ; each of these presents the appearance of an 

 intercellular passage (/), which is surrounded by a layer of larger, 

 thin-walled cells, the epithelial cells. The walls of these cells 

 are brownish ; they contain a large nucleus and a lining layer of 

 protoplasm. To these cells adjoin as a rule starch-containing 

 wood parenchyma cells (a), sometimes also a medullary ray. 

 Their method of development shows that these resin passages 

 arise schizogenously, that is, by the separation of cells originally 

 in union. The resin passages which we have cut in this way in 

 cross-section run vertically through the wood, but are connected 

 together by horizontal ones, which lie within broad medullary 

 rays, and which in the cross-section are occasionally exposed in 



