1904] SPALDING—THE CREOSOTE BUSH 137 
are very slow to become plasmolyzed, or for the most part fail alto- 
gether, in solutions that readily induce plasmolysis of fresh young 
cells and root-hairs near the tip. It was found, however, that some 
of the older root-hairs that are not too far back from the tip exhibited 
plasmolysis distinctly in a 10 per cent. solution of KNO,, but the 
great majority are not affected by this nor by higher percentages. 
In the course of the work it was repeatedly noticed that many of 
the older root-hairs presented the appearance of having undergone 
regeneration, the distal end being clear or semitransparent, in con- 
trast with the dark-colored basal part with its old-looking granular 
contents, the clear terminal portion being irregular in outline and not 
infrequently branched. In the course of experiments on an herba- 
ceous plant, Verbena ciliata, which showed the same phenomenon 
even more strikingly than did the creosote bush, it was found that 
regeneration of its root-hairs could be induced readily by supplying 
with water a plant from which it had been withheld for some time. 
It is probable that this capacity for renewed growth on the part of - 
cells apparently dormant may be an important factor in the absorp- 
tion of water from the soil. 
To sum up briefly the observed facts regarding the absorbing 
cells of the roots of Covillea: Root-hairs are, as a rule, produced 
in large numbers, thus increasing many times the absorbing surface. 
If the plant receives large quantities of water the number of root- 
hairs falls off, and when the roots grow in water none are produced, 
the creosote bush agreeing in this respect with what has been observed 
in land plants generally. The undoubtedly active absorbing tissue 
consists of epidermal cells and root-hairs very near the growing point 
of both primary and secondary roots. These cells fail to show 
plasmolysis with less than 3 per cent. solution of KNO, and are 
readily plasmolyzed with higher percentages; their osmotic pressure 
may accordingly be set down, with more or less variation, as equiva- 
lent to ten atmospheres. : 
The behavior of older epidermal cells and root-hairs is such as 
to throw doubt upon their functional activity as absorbing cells, 
though from their observed habit of regeneration under certain cir- 
cumstances, and from their action with plasmolyzing agents, there are 
