VARKJUS F( J( )D-PLANT8 



^^ 



Fig. 77. — Lettuce. Flower cluster, enlarged. Base of a flower cut vertically 

 to show the single ovule within the ovarj', 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 1)\' union of thefi"\'e anthers. Stjde and stigmas, 

 showing the hairj- region which pushes up through the stamen-tube 

 like a bottle-brush carrying upon it the pollen to be rublied off by insect 

 visitors. (Redrawn from Thonu'.) 



When the raw materials above mentioned are present in a 

 living part containing ehlorojahyll and exposed to sunlight, 

 the energy of tlie sun's rays is utilized to separate the oxygen 

 from tlie carbon and unite tlie hitter with the elements of 

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

 we can detect is usually .starch, but the giving off of oxygen 

 (especially well seeti in a water-plant) is evidence that food- 

 making is in progress. 



Fats and proteids may Ije formed from {'arlxjliydrates in 

 various parts of the plant independently of sunlight; but 

 while fats recjuire only a diminution in the aniount of oxygen, 

 the proteids must have nitrogen, and often sulphur or phos- 

 phorous (derived from the salts above mentioned) coml.iined 

 with tlie carbon, hydrogen, and oxygen of the carl)ohydrates. 

 Dther elem(>nts fountl in tlie iniiieral salts aid in food-making 

 by their mere presence. Thus a minute amount of iron is 

 necessary to tlie formation of chloroiihyll, and potassium 



