66 Knud Jessen. 



often have somewhat curving tangential walls. There are 

 no intercellular spaces in the periderm. The older roots 

 consist mainly of secondary wood with medullary rays of 

 one layer and several cells high which are united with one 

 another by tangential bands of wood-parenchyma containing 

 starch. 



In the young shoot there are 3 — 5 primary vascular 

 bundles. The cambium begins its activity quickly and in 

 the first period of vegetation it forms a considerable quantity 

 of wood. There is no endodermis, as Hollstein also has 

 noticed. Outside the primary sieve-tissue, and afterwards 

 also outside the secondary, bast is developed, usually in 

 isolated groups, rarely as a continuous ring. The secondary bast 

 is often present in less quantity than the primary, naturally 

 enough, as the woody part affords sufficient support. In the 

 Botanic Garden in Copenhagen there always occurred a more 

 strongly developed bast than in plants from more northern 

 regions. The cortex is of simple parenchyma and the epi- 

 dermis is small-celled and has strong outer walls, about 3u 

 thick, with a well-developed smooth cuticle. The pith is 

 heterogenous. There is a peripheral part of active, starch- 

 containing cells and in the central part similar cells form a 

 network between larger and dead cells. The active tannin- 

 containing pith-cells have strong walls. 



Shortly after the cambium has begun to develop wood 

 a phellogen arises in the cortex outside the bast. The first 

 phellogen forms a cylinder which may be closed, but after- 

 wards a typical crust-bark, "Schuppenborke" (cf. Hollstein ) 

 is formed. Each phellogen produces 3 — 4 layers of cork, 

 and each new phellogen-layer cuts off a portion of the secon- 

 dary cortex with the bast-groups or bast-cells enclosed in it. 

 The primary, but dead cortex may be found on the branches 

 even during the third year, and 5 — 6 cork-plates may be 

 counted, separated by dead cortical tissue. 



