74 VARIOUS FOOD-PLANTS 
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Fie. 77.—Lettuce. Flower cluster, enlarged. Base of a flower cut vertically 
to show the single ovule within the ovary, and how the calyx, corolla, 
and style grow out from it above. A single flower. An anther, inner 
view showing openings through which pollen is shed upon the style. 
The stamen-tube formed by union of the five anthers. Style and stigmas, 
showing the hairy region which pushes up through the stamen-tube 
like a bottle-brush carrying upon it the pollen to be rubbed off by insect 
visitors. (Redrawn from Thomé.) 
When the raw materials above mentioned are present in a 
living part containing chlorophyll and exposed to sunlight, 
the energy of the sun’s rays is utilized to separate the oxygen 
from the carbon and unite the latter with the elements of 
water to make a carbohydrate. The first food-product that 
we can detect is usually starch, but the giving off of oxygen 
(especially well seen in a water-plant) is evidence that food- 
making is in progress. 
Fats and proteids may be formed from carbohydrates in 
various parts of the plant independently of sunlight; but 
while fats require only a diminution in the amount of oxygen, 
the proteids must have nitrogen, and often sulphur or phos- 
phorous (derived from the salts above mentioned) combined 
with the carbon, hydrogen, and oxygen of the carbohydrates. 
Other elements found in the mineral salts aid in food-making 
by their mere presence. Thus a minute amount of iron is 
necessary to the formation of chlorophyll, and potassium 
