39 NEW ZEALAND NATURE-STUDY BOOK 
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they do a large surface to the air, are the organs through 
which transpiration chiefly takes place. A green stem is 
responsible to some slight extent for transpiration— 
though this depends a good deal on the stem; a 
woody stem hardly transpires at all. | 
How Roots obtain Food from the Soil. In a 
previous experiment it was shown that the plant food 
must be in solution before it can be absorbed 
by the roots. The rootlets spread out in all 
directions dividing and subdividing in search 
of dissolved plant food. The soil is always 
moist below the surface, even when it appears 
quite dry, a thin film of moisture surrounds 
each particle of earth. ‘The root hairs spread- 
ing out and inserting themselves between these 
particles become so closely applied to them 
Woot ha that the soil water diffuses through their walls 
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adhering and passes up the main roots and through the 
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paruc’s stem as already explained, 
Nott.—This portion of the work might be begun in St. I, or 
indeed earlier, if very simply treated. The first step is to lead 
pupils to see that a liquid can pass into the roots of plants and 
can be conveyed to the leaves—the next is to show that solid 
matter must be dissolved before it can be absorbed—from which 
it follows that available plant-food must be in a. liquid condition. 
So soon as these primary facts have been grasped, pupils will be 
able to understand the meaning of transpiration—how it is 
brought about and its uses. 
The path of the salt-solutions up the stem may or may not be 
taken at this stage—indeed, it might with advantage be deferred 
until dealing with the path of leaf-made food—when the entire 
movements of solutions and assimilated materials could be 
worked out ; this, however, must be decided by the teacher. 
If it (the path of salt-solutions up the stem) be taken in St. I, it 
may require to be done again in the higher classes. 
The uses of transpiration, the rate of transpiration, and the 
process of osmosis or diffusion should certainly be deferred until 
later on in school life, 7.e., should not be dealt with until St. III or 
higher standards be reached. 
