152 PLANT STUDIES 
an active stem be cut and plunged into water stained with 
an aniline color called eosin,* the ascending water will stain 
its pathway. After some time sections through the stem 
will show that the water has traveled upwards through it, 
and the stain will point out the region of the stem used in 
the movement. 
In general, therefore, the carbon dioxide is absorbed 
directly from the air by the leaves, and the water is ab- 
sorbed by the root from the soil, and moves upwards through 
the stem into the leaves. An interesting fact about these 
raw materials is that they are very common waste products. 
They are waste products because in most life-processes they 
cannot be taken to pieces and used. The fact that they 
can be used in photosynthesis 
^9K *&S& s & & ^ == ^r~ shows that it is a very re- 
Jy* ^J markable life process. 
(2) Chloroplasts. Having 
obtained some knowledge of 
the raw materials used in 
photosynthesis, and their 
PIG. 145. Some mesophyll cells from J 
the leaf of Fittonia, showing chloro- SOUrCCS, it IS necessary to 
P lasts - consider the plant machinery 
arranged for the work. In the working leaf cells it is 
discovered that the color is due to the presence of very 
small green bodies, known as chlorophyll bodies or cliloro- 
plasts (see Fig. 145). These consist of the living substance, 
known as protoplasm, and the green stain called chloro- 
phyll ; therefore, each chloroplast is a living body (plastid) 
stained green. It is in these chloroplasts that the work of 
photosynthesis is done. In order that they may work it 
is necessary for them to obtain a supply of energy from 
some outside source, and the source used in nature is sun- 
light. The green stain (chlorophyll) seems to be used in 
absorbing the necessary energy from sunlight, and the 
* The commoner grades of red ink are usually solutions of eosin. 
