31S 



between them. It is enclosed by an epidermal layer of oblong 

 cells, and a subepidermal ring resembling collenchyma. A little 

 farther downward, about 8 mm. from the apex, the most impor- 

 tant change to be noticed is the development of cribrose tissue 

 on the centripetal side of the fibro- vascular bundles. (Later on 

 some much elongated sclerenchymatic cells surround the bicol- 

 lateral bundles on their inner side). In the secondary bark 

 bundles of young "bast- fibres are detected. In the primary bark 

 large air-spaces, much elongated in the direction of the axis, have 

 been formed by the separation of the parenchyma cells. 



The development of the different tissues continues in the 

 manner indicated, and on cross-sections about 8 cm. from the 

 apex, where the swelling of the stem is just about noticeable, we 

 find the primary bark traversed longitudinally by numerous 

 air-channels resembling those of so many aquatic plants (ch. 

 figs- 2, 3, 4, 6, 7). Sometimes the cells of this lacunar bark 

 elongate so much, especially in a radial direction, and their con- 

 nection becomes so loose, that it resembles, to some extent, the 

 floating-tissue described above. 



At the inner border of the primary bark is a ring of isolated 

 groups of typical bast-fibres surrounding the phloem, (bf Figs. 2, 

 3, 4,) and in the narrow zone of parenchyma between the bast-fibre 

 bundles and the groups of sieve-tubes we meet with a new tissue- 

 element. Many of these parenchyma cells have been divided by 

 a tangential partition (m. Fig. 2) at first an irregular interrupted 

 ring of meristem is formed, then the gaps are gradually filled up, 

 and a closed ring is developed between the cribrose zone and the 

 groups of bast-bundles, very much resembling the secondary 

 phellogenetic layer of many barks, (m. Figs. 3, 4, S). This 

 meristem at first produces, in a centrifugal order, a few rows of 

 oblong, flat cells. In the outer rows the cells soon become 

 rounded off at the longitudinal edges so that most of them cohere 

 only shghtly along the middle of their tangential surfaces. Now, 

 here and there, a cell in the outermost row begins to bulge out 

 in the middle of its outer tangential wall, thus producing a short 

 pillar that presses against the cells situated still farther toward 

 the periphery (1. Figs. 3, 4). The same change takes place in 

 the layer underneath, toward the initial meristem. Each cell 



