18 



DESCRIPTIVE BOTANY. 



PART I. 



reticulated ; whilst it sometimes happens, that the coils 

 of a closely developed 

 spiral become sepa- 

 rated at intervals, 

 and then close to- 

 gether again, so as to 

 leave openings which 

 look like slashes and 

 dots in the vesicle itself (c). There are some cases, how" 

 ever, in which the dots on the vesicles appear to b e 

 thickened spots ; and especially those which abound 

 on the elongated cells, forming the woody fibre of 

 Coniferous, and some few other trees. These are very 

 peculiarly marked by large dots of a glandular aspect, 

 with a dark spot in the centre (fiy. {).) ; which latter 

 circumstance, however, may probably be owing to the 

 manner in which the light is refracted 

 through them. It is a remarkable fact, 

 that these appearances are strictly imitated 

 in many fossil woods ; and botanists are 

 thus enabled, by the inspection of a small 

 fragment of such plants, to pronounce with 

 certainty, upon the!Class and Order to which 

 they have belonged. In some cases it hap- 

 pens, that the elementary fibre alone remains 

 entire, like a skeleton to the tissue, whilst 

 the membrane which originally formed the walls of the 

 cells has been obliterated. It is unnecessary to dwell 

 further upon the various appearances which the cellular 

 tissue presents, especially as nothing whatever is known 

 of the way in which a dissimilarity of structure, is con- 

 nected with any modification in the functions performed 

 by it. 



(19-) Contents of the Cells. The cellular tissue is 

 every where replete with juices, containing minute gra- 

 nules of amylaceous, resinous, and other qualities, 

 which appear to be the result of peculiar secretions, 

 formed by the vesicles themselves. Those which com- 

 pose the woody fibre, secrete an abundance of a car. 



