VEGETABLE PHYSIOLOGY. 



[LESSON 9. 



FIG. 48. 



FIG. 49. 



Vessel becoming annular. 



To substantiate these opinions, the following series of illustrations, 

 drawn from existing preparations, are offered. 



181. The first stage of the process of disintegration appears to be 

 a concentration of the spiral element into a filament of greatly in- 

 creased robustness (Fig. 48) ; the newly formed spiral then throws 



itself into a loose and irreg- 

 ular coil within the cell, the 

 parietes (sides) of the latter 

 becoming at this period par- 

 ticularly distinct; the ter- 

 minations of the filament ex- 

 hibit a tendency to form 

 rings, which having done, by 

 a process of absorption, they 

 are cut off, and separated by 

 an interval of space. This 

 process continues till the en- 

 tire tube contains only a se- 

 ries of rings, more or less 

 widely separated (Fig. 49), 

 now called annula, from anellus, a little ring. 



182. The process of gradual decadence (decay) does not stop 

 here. It is very easy, by long continued maceration in water, to 

 separate these rings from the tubular envelope, for they, being com- 

 posed of woody fibre, can resist the action of water, to which the 

 tubes of cellulose must speedily succumb. These rings, thus obtained, 

 are shown at Fig. 50. In this view of them it will be seen that they 

 are not round, but compressed rings, with a variable number of 

 angles. 



183. It is easy to understand that the process of absorption, al- 

 ready in operation to produce a series of rings out of a continuous 

 spiral thread, does not necessarily cease, and such appears to be 

 the fact. 



184. One of the rings (A), has been divided into eight portions, 

 to show the like separation which occurs in nature ; absorption and 

 concentration having firstly formed the irregular filament, and second- 

 ly divided it into a series of distinct rings, still continues, by divid- 

 ing the rings respectively, all of them remaining in situ (situation, 

 place), and removing a portion of each divided fragment rounding 

 its extremities till a scalariform vessel (Fig. 51) results. 



