THE STRUCTURE OF THE ROOT 



17 



denser body, richer in albumen than the general mass of proto- 

 plasm, and called the nucleus (Fig. 5 a). Within the latter 

 we see one or more refringent bodies, the nucleoli (Fig. 5 &). 

 These delicate meristematic cells, which are constantly dividing, 

 and are thus producing the elements of new growth, become 

 larger and more transparent the farther they are removed from 

 the actual apex. At the point where the first root-hairs are 

 developed, the cells of the region B in Fig. i will already have 

 the appearance of the right-hand cell of Fig. 6. Here the 

 viscid mass of protoplasm no longer occupies the entire cell 

 space or lumen. It still forms a thick lining {'primordial iitride) 

 on the inside of the cell-wall, as can be seen in every parenchy- 



FiG. 5.— Young (Meris- 

 tematic) Cells with 

 Nuclei. 



a, nucleus ; b, nucleolus. 



Fig. 6.— lOUNG PARENCHiMATOlS CELLS. 



matous cell as long as it continues to live. But in the centre 

 of the viscid protoplasmic mass spaces (vacuoles) (Fig. 6 a) 

 have made their appearance, and these are filled with a watery 

 cell-sap. As the cell grows, the vacuoles become larger and 

 more numerous, and the mass of protoplasm separating them 

 consequently thinner and thinner, until they present the ap- 

 pearance of delicate threads of protoplasm suspending the 

 nucleus in the centre of the cell (Fig. 6 z). Finally, °these 

 threads too break across (Fig. 6 b), the cell then contains a 

 large central vacuole, and the nucleus with its nucleolus (Fig. 

 6 k) slides towards the cell-wall, which is now evenly lined 

 by the primordial utricle (Fig. 6 c). 



Cells in this condition, as we find them, for instance, in the 

 older portions of the root cortex, are able to store up other 



B 



