22 THE PLANT CELL. 



mass of the protoplasm, the former preponderating ; at this stage 

 the nucleus is usually embedded in a central mass of protoplasm, 

 whilst " bridles " of varying breadth pass from this mass to 

 a layer of protoplasm lining the cell-wall internally. In still 

 older cells the protoplasm forms a layer lining the wall, and 

 encloses a central vacuole, the nucleus lying somewhere in this 

 peripheral layer. 



Starting from the young undifferentiated cell as the simplest 

 type many subsequent modifications are to be found, and in the 

 following pages the main object will be to study in detail the 

 changes in structure, size, and function which occur in cells of 

 different parts of plants, according to the position thej' occupy 

 and the conditions brought to bear upon them. 



Note. — The permanent microscopical preparation of the young cell is 

 readily carried out by first "fixing" a root-tip or other embryonic tissue 

 in Flemming's solution (see note at end of Chap, viii.), washing, after 

 fixing, in distilled water for some hours, and then hardening in alcohol, 

 and transferring to methylated spirit ; sections, either longitudinal or 

 transverse, should then be made from this, and these stained with 

 hcematoxylin (Delafield's) and fuohsin, using the stains in dilute solution, 

 and staining with each separately. The section is then dehydrated with 

 alcohol and spirit, cleared with clove-oil, and mounted in xj'lol balsam 

 (Canada balsam thinned with a little xylol). Very beautiful preparations 

 may be made by this method. 



