85 ELEMENTARY TISSUES. 



' 



OBSERVE: 1. If there is a larger amount of air imprisoned in 

 one preparation, than in the other. 



2. The form, and color of the cells, their thin walls resem- 

 bling the parenchyma previously studied. Apply concentrated 

 chromic acid to the section and note the effect. Suberin will enable 

 the cork to resist for a long time, (often many days and perhaps 

 continuously) , the action of the acid, while all other modifications 

 of cellulose are readily dissolved by it. 



The probable absence of cellulose from suberized walls, as pre- 

 sented by Eugene Gilson, is interesting to note in this connection, 

 (La suberine et les cellules du liege. La Cellule, etc., p. p. Carony, 

 T. 1890 p. 63.) See Zimmermann's Microtechnique, p. 148. 



MODIFICATION OF CELL WALLS. 



Those .that produce changes in the chemical composition of the 

 cell wall may be classified as follows: 



1. Mucilaginous Modification. 



2. Ligniftcation. 



3. Cutinization. 



4. Mineralization. 



Illustration First: Cell walls containing MUCILAGE. SEED 

 COATS of FLAX or LINSEED. 



Make a thin tangential section of the seed, and place for a few 

 minutes in water. 



OBSERVE: 1. The ready absorption of water, and consequent 

 thickening of the cell wall. 



2. Its gelatinous consistence in seeds that have been left for 

 some time in water. 



In many cases the modification goes so far as to convert the 

 cell wall into a gum, soluble in water. Examples of this can be 

 found in the Plum, Cherry, or Peach trees. Vines' Text Book of 

 Botany, p. 107; Goodale, p. 34; Strasburger, pp. 99, 340. 



Illustration Second : Cell walls containing LIGNIN. Fibrous 

 tissue of the stem of any woody Phanerogams, or Vascular 

 Cryptogams. 



Make a thin section of a woody stem and Amount in a few drops 

 of cuprammonia. Note the walls are not dissolved, which would 

 be the case, if they were pure cellulose. (P. 5.) 



To a fresh section add iodine and sulphuric acid, or chlor- 



