158 
Each of the mineral 
ROOTS 
salts which plants require, apparently, 
is so specially related to the nutrition of the plant, that not one 
of them can be omitted, although all others are present in 
ui- f 
4 Qa 1 BZ By 
Fig. 139.—Water cultures 
of Buckwheat, showing ef- 
fect of the lack of the dif- 
ferent mineral elements: 
1, with all the elements; 
2, without potassium; 3, 
with soda instead of potash; 
4, without calcium; 5, with- 
out nitrates or ammonia 
salts. 
suitable quantities. This fact is dem- 
onstrated by growing plants with their 
roots in distilled water to which the dif- 
ferent mineral salts can be added in such 
proportions as the experiment demands. 
When the salts are added in such pro- 
portions that the solution imitates a soil 
solution, such as ordinary spring or well 
water, many herbaceous plants are able 
to grow in it till they have flowered and 
produced seed. In fact, aside from the 
lack of anchorage and having to supply 
their roots with oxygen from the shoot, 
plants may do almost as well as when 
rooted in the soil. For some plants the 
water culture gives good results, when 
the salts are in such a proportion that 
2 liters of the solu- 
tion contain 1 gram 
of potassium nitrate, 
4 gram of iron phos- 
phate, + gram of cal- 
cium sulfate, and } 
gram of magnesium sulfate. The results of 
omitting some of these salts are shown ‘in 
Figure 139. 
Root Absorption. — For the process of os- 
mosis upon which the entrance of water into 
the root depends, the epidermal cells of the 
root tip are especially fitted. By means of 
the root hairs they have a large surface in 
contact with the soil solution. Having thin 
cellulose walls against which their protoplasm 
Fic. 140. — Root 
hair showing the thin 
layer of protoplasm 
and large vacuole. 
After Frank. 
is spread out into a thin lining, root hairs afford an easy entrance 
of water into their large vacuoles. (Fig. 140.) As the student 
already knows from his acquaintance with osmosis, the entrance 
of water into the epidermal cell depends upon the concentration 
