CHAPTER IV 



THE CHEMICAL REACTIONS OF PLANT 

 TISSUES 



The minute details concerning the composition 

 of cell walls and cell contents are often of great acade- 

 mic interest, although the microanalyst depends 

 more upon structures than upon specific chemical 

 reactions. However, there are instances when these 

 reactions are of practical value. Certain complex 

 organic substances occur in all plants either in the 

 cell walls or the cell protoplasm. Variations in the 

 amounts or combinations of these compounds materi- 

 ally influence the structure of different tissues. While 

 the original walls of the embryo cells are thin and 

 consist largely of cellulose, when the plant assumes 

 an independent existence other substances are depos- 

 ited or added to this cellulose wall with consequent 

 thickening or other changes in appearance. In deal- 

 ing with the chemical constitution of plant tissues 

 it is convenient to consider the relations of the cell 

 apart from those of the cell contents. This is all 

 the more desirable because the compounds present 

 in cell walls are relatively few as compared with 

 those possibly present in the protoplasm and those 

 which result from the physiological activity of the 



latter. 



57 



