150 PLANT RELATIONS. 



color. It has been stated that this green color is due to 

 the presence of a coloring matter known as chlorophyll 

 (see §12). The two groups may be spoken of, therefore, 

 as (1) green plants and (2) plants ivithout chlorophyll. 

 The presence of chlorophyll makes it possible for the plants 

 containing it to manufacture their own food out of such 

 materials as water, soil material, and gases. For this 

 reason, green plants may be entirely independent of all 

 other living things, so far as their food supply is concerned. 



Plants without chlorophyll, however, are unable to 

 manufacture food out of such materials, and must obtain 

 it already manufactured in the bodies of other plants or 

 animals. For this reason, they are dependent upon other 

 living things for their food supply, just as are animals. It 

 is evident that plants without chlorophyll may obtain this 

 food simply either from the living bodies of plants and ani- 

 mals, in which case they are called parasites, or they may 

 obtain it from the substances derived from the bodies of 

 plants and animals, in which case they are called sapro- 

 phytes. For example, the rust which attacks the wheat, 

 and is found upon the leaves and stems of the living plant, 

 is a parasite ; while the mould which often develops on stale 

 bread is a saprophyte. Some plants without chlorophyll 

 can live either as parasites or saprophytes, while others are 

 always one or the other. By far the largest number of 

 parasites and saprophytes belong to the group of low plants 

 called fungi, and when fungi are referred to, it must be 

 understood that it means the greatest group of plants with- 

 out chlorophyll. 



112. Photosynthesis. — The nutritive processes in green 

 plants are the same as in other plants, and in addition there 

 is in green plants the peculiar process known as photosyn- 

 thesis (see §25). In plants with foliage leaves, these are 

 the chief organs for this work. It must be remembered, 

 however, that leaves are not necessary for photosynthesis, 

 for plants without leaves, such as alga?, perform it. The 



