PASSAGE OF WATER: THROUGH. THE PLANT: 110 
CHAPTER XVII 
THE PASSAGE OF WATER THROUGH oe PLANT 
Necessity of WATER is essential to the lite of every organism, 
Water. whether plant or animal; it enters into the 
composition of the protoplasm and cell-wall, and therefore 
must form part of the food of the plant; no vital process 
can go on without it, growth cannot take place without 
it, and in very many cases it is essential to reproduction. 
In certain Flowering Plants, pollen grains are conveyed by 
water, and in many cases it 1s an agent for the dispersion 
of seeds. | 
It is a matter of common observation that plants will die 
without water. In this chapter we will consider how water is 
taken in by the plant, and its passage through the plant, 
leaving its connection with respiration and other vital pro- 
cesses until later. | 
Take a seedling and fit it into a hole in the 
cork of a glass bottle containing water, in such a 
way that the roots dip into the water. Mark the level of the 
water in the flask. | 
Result. ~ After some time the level of the water falls. 
Conclusion. ‘The plant is taking in water through its roots. 
The question then arises, How is it that water can pass into 
the roots? We have already noticed (Chapter II.) that root- 
tips are covered with root-hairs ; it is these that drink in the 
water and pass it on to the cells of the root. The root-hair of 
a flowering plant usually consists of a cell with a cell-wall, so 
that the question now narrows itself to this: How can water 
pass through the cell-wall? The following experiment illus- 
trates the nature of the process : 
- Experiment I, 
