4f20 Prof. H. Karsten on the Furmation, 



& 39). It is only at the spot where it formed an annular fold, 

 in consequence of its depression, that it is any longer visible, 

 very strongly thickened, often in layers. 



In the course of the further development and outgrowth of 

 the adjoining living cell, this membrane of the inverted cell, 

 which thus serves the living cell as an external envelope com- 

 parable to a cuticle, is absorbed in the same way as the inter- 

 mediate substance and cortical tissue which is dissipated before 

 an adventitious root. (See my account of the Organs of Vegeta- 

 tion of the Palms, pi. 4, fig. 8.) 



This absorption of the inverted septum (figs. 37, 38, 39, & 

 43 a, b) proceeds from below upwards (from the centre towards 

 the periphery), in such a manner that the rather thick fold is, at 

 a certain phase of development, the sole indication of the dis- 

 placed septal wall ; it then surrounds and somewhat constricts 

 the daughter cell, in the form of an annular fibre, within the 

 enveloping membrane (fig. 42 a ; the immediately preceding stage 

 of this fold is represented at b) . 



This structural condition occurs not only in the course of 

 artificial prei)arations, but also very frequently as a consequence 

 of injuries in the course of the natural growth of the plant. 

 These annular folds, when their origin is not recognized, may 

 easily be mistaken for those others which have been regarded 

 as incipient and suppressed septal structures. 



The remaining cylindrical dead wall of the cut joint-cell 

 sometimes presents a delicate, though very definite, longitudinal 

 striation (figs. 31, 33, 35). 



Not unfrequently, moreover, a cell is prolonged, in the manner 

 described, through two or more adjoining cells, on account of 

 circumstances operating prejudicially on their vitality ; and we 

 then find on the surface of these long joint-cells several annular 

 folds situated at distances determined by the length of the 

 original cells. 



It is the general, but not universal rule, that the development 

 of isolated joint-cells proceeds in the manner illustrated in figs. 

 33, 34, & 35, the adjoining dead cell-wall being regularly and 

 equally invaded by the growing cell, and apparently expanded 

 passively. At times one side or one portion of the septum ap- 

 pears to ofi'er greater resistance than the rest, or else the vegeta- 

 tive energy of the extending cell is more considerable on one 

 side than in the median line ; and the consequence is the pro- 

 duction of irregular forms of the annular rings, as exhibited in 

 figs. 37 & 39 a. 



It also now and then happens that the growing cell, when it 

 has just advanced into the cavity of the cut cell, does not thrust 

 the whole area of the septum downwards before it, but, as shown 



