134 HOFMEISTER, ON 



very narrow and elongated (PI. XVII, figs. 8, 9) . Lastly, the 

 cells of the bark, in all tolerably vigorous shoots, divide 

 once more by tangential longitudinal septa, and in all cases 

 very frequently by transverse septa (PL XVII, fig. 8). 

 The bark thus becomes a stratum, consisting of from two 

 to four layers of cells. In slender shoots this duplication of 

 the cellular layers of the bark does not take place ; trans- 

 verse divisions only occur in their cells, so that even the fully 

 grown bark consists of only one layer of cells. 



A considerable thickening takes place in the walls of the 

 cells of the axile tissue of the ends of the stems of fully formed 

 shoots, whose longitudinal growth remains dormant from the 

 end of autumn until the following spring, and whose densely 

 crowded lateral shoots form a capitate accumulation round 

 the end of the stem. This thickening is observable in a 

 transverse section, when made about ten cells underneath 

 the terminal bud. The thickened cell-membranes exhibit 

 delicate pits (PL XVII, figs. 9, 9 h ), which bring to mind 

 those of the Coniferae, inasmuch as they are usually 

 (not always) arranged in longitudinal rows.* There are 

 not any lenticular air-cavities between the ends of two con- 

 tiguous pits j the ends are divided from one another by a 

 thin, apparently homogeneous, membrane. The pits, when 

 seen from the surface, exhibit within their circumference a 

 narrow oval, but this appearance is probably caused by an 

 interference of the rays of light incident from beneath. 

 During the final longitudinal growth of the stem, during 

 the remarkable expansion of the axile tissue of the inter- 

 nodes (which expansion is rarely accompanied by a trans- 

 verse division), the thickening of these cell-membranes for 

 the most part disappears. In old stems the membranes of 

 the middle cells become rather thin again, and less brittle 

 than in the younger portions. It is now difficult to dis- 

 tinguish any traces of the pits, which at an earlier period 

 were so distinct. They have now the form of short, oblique 

 fissures. The above-mentioned peculiar thickening of the 

 cell-membranes only extends a short distance into the axile 



* Figures of these pitted cells, agreeing with those previously published by 

 me, have also been given by 'Schimper, M6n. pres. p. div. savants,' xv, pi. iv, 

 f.4. 



