s 



78 Knud Jessen. 



Bast-tissue is absent from the rhizome; it is most vigor- 

 ously developed in the stem where it forms a continuous 

 cylinder outside the sieve-tissue; the bast is connected with 

 the secondarily formed portions of stereom in the outer part 

 of the groups of wood by the lignified medullary rays. The 

 stolon also contains bast abundantly: it is more slightly 

 developed in the thickened apex. 



In the rhizome a continuous cambium forms a conti- 

 nuous woody portion which shows distinct annual rings. 

 The numerous medullary rays are 1 — 3-layered and upwards 

 of 20 cells in height. In the stem there is no continuous 

 cambium except in its basal part; on the other hand a con- 

 tinuous cambium begins to function early in the thickened 

 apex of the stolon. 



While the cortex in the stem is distinguished into an 

 outer small-celled part filled with chlorophyll and an inner 

 larger-celled part poor in contents, the whole cortex in 

 the apex of the stolon functions as food-storing tissue, and 

 is crowded with starch in the autumn. The 1 — 3 outer cor- 

 tical layers are collenchymatous especially in the erect stem. 



The pith is heterogeneous as in all the Rubus-species 

 hitherto investigated (cf. Fkitsch). The active cells, espe- 

 cially the starch-containing ones in the rhizome and the 

 apex of the stolon, are found chiefly in the periphery of the 

 pith, but also in addition dispersed longitudinal rows of 

 living cells occur in the central part which for the rest con- 

 sists of larger dead cells. Anastomoses are rare. 



During autumn the quantity of starch diminishes in the 

 different tissues of the rhizome and at the same time large 

 quantities of fat may be demonstrated. 



The leaves are slightly hairy on both sides and are 

 somewhat folded. No glandular hairs were found. On the 

 lower surface the bundles are very prominent. The structure 

 is mesophilous in correlation with the fact that the leaf lives 



