thp: assimilating cell. 



21 



brown by iodine solution, since no starch has as yet been formed 

 in them ; at times, however, starch may be formed in them by 

 a different process to that which takes place in chloroplasts, the 

 available energy for this being derived not from light rays, but 

 some other source. 



The general shape of the young cell is in section often oval, or, 

 if there is much lateral pressure due to other cells, polyhedral ; 

 thus, if the pressures are equal in every direction, and the cells 

 of equal size, the geometrical shape of a cell is that of the regular 



Fig. Qa.—A Photomicrograph showing Young Cells of the Endosperm 

 OP Ccdtlut palustris. — Bridles of protoplasm are to be seen passing 

 between adjacent cells. 



dodecahedron ; but, as a rule, the pressures are not always equal, 

 and since the cells are not always of the same size, the shapes met 

 with are often irregular (see Fig. 5). 



As growth proceeds, the cell-sap which exists in the meshes of 

 the protoplasm gradually collects into vacuoles, this being due to 

 the relatively unequal growth in volume of the cell-cavity and in 



