CHAPTER III 
THE INFLUENCE OF WATER ON PLANT-LIFE 
Water is the most important factor in ecology. In con- 
junction with heat, it determines climate. It plays a 
dominant part in the life and well-being of every individual 
plant, and decides the form and character of the vegeta- 
tion everywhere. Where water fails, there is no vegeta- 
tion; where it is most abundant, there the vegetation is - 
most luxuriant and varied. 
The Role of Water in Plants. 
1, Water is the medium which conveys to all parts of 
the plant-body the materials required for its nutrition 
and growth. These must be in solution, for solid particles 
cannot pass through the tissues of plants. These sub- 
stances are, for the green plant : 
(a) Mineral salts, absorbed by the roots from the soil, 
and destined to be employed in the elaboration of 
food ; and 
(6) The food itself (carbohydrates, proteins, etc.), con- 
veyed in a watery sap to every living part of the plant 
—to the points of growth, to the centres of work, or to 
the seats of storage. 
2. The body of the plant is nearly all water. In a 
living cell which has reached its full size, the living 
substance, or protoplasm, is little more than a thin skin 
lining the wall. The rest is sap, a watery liquid con- 
taining nutriment and other substances in solution. 
3. Moreover, the living cell can only keep in health 
and perform its functions successfully while it is turgid, 
or stretched with water. As soon as the cells lose their 
turgidity, the leaves and shoots become limp and droop, 
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