74 



VARIOUS FOOD-PLANTS 



Fig. 77. — Lettuce. Flower cluster, enlarged. Ba.se of a flower cut ^•e^tically 

 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 Thome.) 



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 Avith the elements of 

 water to make a carbohydrate. The first food-product that 

 we can detect is u.sually 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 car])oh3-drates 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 



