1904] SPALDING—THE CREOSOTE BUSH 135 
Much the same difficulty was experienced with seedlings grown 
in soil. In some cases the root-hairs arise thickly in complete zones, 
the rest of the root being free from them; in other cases, while they 
are abundantly produced, their distribution is extremely irregular; 
and in still other specimens of the same lot of seedlings the root is 
nearly naked, there being almost no root-hairs whatever. 
In examining a large number of seedlings grown under different 
conditions other possibly important data in regard to this matter 
have been obtained, but for our present purpose it is sufficient to 
emphasize the well established fact that the roots of Covillea, whether 
growing in the lighter soil of the mesa or the heavier soil of the labora- 
tory hill, ordinarily produce great numbers of root-hairs, and that 
their number becomes less if the plant is given a very large quantity 
of water. If grown directly in water root-hairs are altogether wanting. 
Whatever other conditions, then, may or may not afford the stimulus 
that results in the production of root-hairs in general, the quantity 
of water in the soil is, in the present case, a factor of prime importance. 
There is no doubt that the epidermal cells of the root of Covillea 
which would retain their original form if abundantly supplied with 
water do, as a matter of fact, promptly increase their surface greatly 
by pushing out root-hairs if the water supply is suitably diminished. 
Whether in this process the epidermal cell responds directly to the 
diminished supply of water in the soil around it, or to conditions 
arising from lack of water in the plant of which it is a part, is a ques- 
tion of theoretical interest well worthy of special investigation. 
The epidermal cells near the tip of the root, whether prolonged 
into root-hairs or not, function as the living agents of absorption. 
To what extent the older root-hairs may function in the same way, 
or may serve rather to soak up water like a sponge, when there is an 
abundant supply, is a question reserved for fuller discussion than can 
be entered into here. We are now concerned, first of all, with the 
degree of force with which the undoubtedly vital agents of absorption, 
the living cells near the root-tip, absorb water from the relatively dry 
soil in which, as we have seen, the creosote bush maintains itself alive 
and keeps up its transpiration “‘stream.”’ 
In the investigation of this subject, which is still in progress, seed- 
lings of Covillea, of different ages were carefully removed from the 
