358 



THE MICROSCOPE. 



to enclose another in a shrivelled condition ; this state is 



sometimes so far extended, that a thick granular cord is 



all that can be seen of the contents. 



" The period of growth at which the laying down of 



fibre commences, determines the distance between the 

 several coils; for instance, when it is 

 first formed, the coils are quite close, 

 scarcely any perceptible trace of mem- 

 brane existing between them. In the 

 annular vessel, the development of 

 the cell and the adherence of the 

 granules to each other are conducted 

 in the same manner ; the deposit 

 showing a tendency towards the spiral 

 direction, by the presence of a spire 

 connecting two rings, or by a ring 

 being developed in the middle of a 

 spiral fibre. The annular vessel is 

 the first observed in the youngest 

 parts of plants, and when found alone 



Fig. 202. _,* section from indicates a low degree of organisation; 

 the stem of a coniferous as shown by its occurrence in Spha- 

 ffi&5&5^ 9*> Equuetum, and Lycopodmm, 

 the zones of annual w hich plants, in the ascending scale of 



growth, annual rings. f. , . , , X , 



vegetation, are almost the first that 

 possess vascular tissue. 



" It will be found that spiral fibre occurring with rings 

 marks a higher step in the scale of organising power; the 

 true spiral more so; and the reticulated and dotted mark 

 the highest ; this being the order in which these several 

 vessels are placed in herbaceous exogens proceeding from 

 within outwards, the differences of structure of the several 

 vessels being indices of the vital energy of the plant at 

 the several periods of its development. In those vessels 

 in which the annular or spiral character of the fibre is 

 departed from, some curious modifications of the above 

 process are to be observed, as in the reticulated vessels 

 met with in the common balsam (Salsamina hortensis). 

 The primary formation of fibre in these vessels : s marked 

 by the tendency of the granules to take a spiral course, 

 when it happens that some one of the granules becomes 



