319 



directly under the one that produced the pillar-like process sends 

 out a similar excrescence (fl. Fig. 3), and by the united pressure 

 of all the rising columns the cells of the outerpiost row are sep- 

 arated from the layer underneath, are raised in a body, and now 

 lorm a kind of ceiling supported by the numerous rapidly 

 elongating columns inserted in the floor consisting of the cells of 

 the next inner layer (Figs. 3, 4. 5, 7). This process is repeated 

 with the third and all the successive layers pushed outward by 

 the activity of the meristem, so that in a short time this tissue 

 assumes the characteristic appearance described above. The 

 loosening and raising of the various layers does not take place all 

 around the stem at the same time, but only over a limited area 

 in the centre of which the columns become tallest, so that an 

 arched ceihng is formed. Then another conticruous arch arises 



leaning against some portion of the former, etc., consequently 

 the arrangement of the layers is not strictly concentric. 



The cells outside of this newly formed tissue are, of course, at 

 once affected by the increasing outward pressure. The bast- 

 bundles with the lacunar primary bark are raised (Figs. 3, 4) and 

 forcibly torn away from their connection with the phloem part of 

 tne stem. The loosely cohering parenchyma cells of the outer 

 bark cannot resist the radial pressure, it is burst open longitudi- 

 nally in different places, and either adheres in narrow strips to 

 the floating tissue, or is thrown off. The bast- fibres are either 

 pushed outward, retaining their connection as entire bundles, or, 





by the unequal pressure of the elongating columnar cells they 

 ^re separated from one another and are found scattered about 

 among the outer layers of the floating tissue, or else are thrown 

 off with the primary bark. 



Ihe floating tissue usually accommodates itself to the increase 

 of the circumference by the tangential elongation of the cells 

 forming the successive '* floors.*' Frequently, however, it is rent 

 by longitudinal clefts similar to those appearing in the old bark 

 01 trees. The structure of this tissue is often quite intricate, for 

 oesides the *' floor-beams " placed in various directions within 

 the same horizontal plane, parallel to the surface, there are 

 numerous strands of elongated cells running obliquely across 

 several tiers (Fig. 7) connecting and bracing them like the lattice 



