THE STEUCTUEE OF THE EOOT 



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 6). 

 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 rq|)t-hairs are 

 developed, the cells of the region R 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 utricle) 

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



7^ 



Fia. 5.— YOUHG (Mekis- 

 TEMATio) Cells with 

 Nuclei. 



a; nucleus ; b, nucleolus. 





II ^ 



Fig. a— Young pakenohymatous' Ceils; 



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 h), the cell' then contains a 

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

 6 A>) 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 ihsttoce, in the 

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



B 



