214 PHYSIOLOGICAL BOTANY. PART II. 



in the juices of plants. After it has been formed 

 it is again very easily altered during the progress of vege- 

 tation; a fact of considerable importance to the cultivator, 

 who must be cautious to collect the produce of his canes 

 at the season when the sugar is most abundantly gener- 

 ated and before it sustains such alteration. The flowering 

 of the cane exhausts the sugar in the stem; and that 

 which is so abundantly contained in the cortical sys- 

 tem of the root of the beet is ultimately carried into 

 the upper parts of the plant, and similarly exhausted 

 during its inflorescence. 



(200.) Lignine. This substance is contained in 

 the elongated vesicles termed closters(art. 1 6. fig. 3. c), of 

 which the woody fibre is composed. It does not ap- 

 pear that it has ever been submitted to a careful analy- 

 sis, or accurately examined in a detached form. After 

 various matters have been abstracted from the woody 

 fibre, such as certain salts, gummy particles, and others, 

 there then remains about 96 per cent, of an in- 

 soluble substance, composed of nearly equal propor- 

 tions of water and carbon. But this is a compound 

 material, consisting both of the thin pellicle which 

 formed the vesicles themselves as well as of the lignine 

 which they contained. The resemblance which lignine 

 bears to gum is not so striking as in the case of the two 

 materials just described, nor does it appear to answer any 

 ulterior purpose of nutrition after it has become secreted ; 

 but it remains unchanged in the cells, and imparts 

 to wood the varied qualities and colours which different 

 species present. Its specific gravity varies being 1-459 

 in the maple, and 1 -.5.34 in the oak. 



(201.) Vegetable Products. Besides the four ma- 

 terials gum, fecula, sugar, and lignine, which we 

 consider as the simplest modifications which the nutri- 

 tious and organisable materials found in the vegetable 

 structure can assume, there is an interminable catalogue 

 of other substances which may be extracted from the 

 juices of different plants, all of which have been formed 

 by secretion in some part or other of their structure. 



