46 Principles of Plant Culture. 



The supplying of food material is not the only office 

 performed by water in the plant. The unfolding and 

 expansion of the plantlet is largely due to a strong ab- 

 sorptive power for water possessed by the protoplasm 

 within the cells. This force causes all living parts of 

 plants to be constantly saturated with water. Indeed, 

 it distends the elastic cell-walls with water until they 

 are like minute inflated bladders. The pressure thus 

 set up aids in unfolding the different parts from their 

 snug resting-place within the seed-case and enables the 

 plantlet to stand erect. Growth by cell division, it is 

 true, begins rather early in the germination process, 

 but this cannot take place unless the cells are first dis- 

 tended with water (29). A sufficient amount of water 

 is absolutely necessary, therefore, to growth in plants. 

 Foliage wilts in dry weather because the roots are un- 

 able to supply enough water to properly distend the 

 cells ; gi owth is impossible in plants of which the foliage 

 is wilted. When the water supply is abundant on the 

 other hand, and the absorptive power of the roots is 

 stimulated by a warm soil (101), the pressure within 

 the cells often becomes sufficient to force water from 

 the edges and tips of leaves. The drops of water that 

 so often sparkle on foliage in the sunlight of summer 

 mornings, commonly mistaken for dew, are usually 

 excreted from the leaves. In young plants of the cala- 

 dium, water is sometimes ejected from the leaf -tips 

 with considerable force. 



The water of plants is almost wholly absorbed by the 

 root-hairs (100), the leaves having no power to take up 

 water, even in wet weather. The water of plants, with 



