28 BOTANY OF THE LIVING PLANT 



of the cell-wall itself. The encysted state of the cell is a feature of all 

 advanced types of Plant-Organisation. It was probably secondary 

 in origin, and its existence is amply justified by the strength and 

 protection which it affords to the defenceless protoplast. Moreover, 

 it has made possible the building up of large mechanically stable 

 plant-bodies, whether buoyed up in water or supporting themselves 

 in air. The presence of cell-wall may appear to have complicated 

 the problem of physiological interchange by interposing barriers 

 between the protoplasts. But this difficulty has been surmounted 

 by those threads of protoplasm, which traverse the walls, and link 

 up the protoplasts into a continuous living system. 



