PLANTS AND ANIMALS 45 



20) and in other groups the motile phase is dominant. On the 

 whole there seems to be little justification for continuing to regard 

 these chlorophyll-bearing flagellates as animals or for retaining 

 them with the protozoa. 



The Mystery of Chlorophyll 



What is this chlorophyll that is so distinctly a plant char- 

 acteristic? It would not be overstating the matter to say that 

 chlorophyll is the most important type of substance in nature, 

 and that without its activity animal forms would quickly perish. 

 The food of animals if traced back along any line, would finally 

 bring us to chlorophyll-bearing plants and to bacteria. Man, 

 for example, is practically omnivorous, taking his food directly 

 from the plant kingdom in his vegetables and cereals, and from 

 the animal kingdom in his beef, mutton, fish, and fowl. Cattle, 

 sheep, and birds, in turn, obtain their main nourishment from 

 plants. Birds, it is true, eat worms and insects to a great extent, 

 but since worms and insects feed on leaves and vegetables, this 

 food is only one step removed from green matter. Man eats 

 fish, oysters, and other marine food; the larger fish eat smaller 

 ones, and so on until the smallest eat Crustacea, larvae, protozoa, 

 and other micro-organisms which finally subsist on microscopic 

 algae and upon bacteria. Back of it all is the mysterious activity 

 of chlorophyll. And yet chlorophyll is not a living substance. 

 It is a product of the activity of certain parts of living plant 

 protoplasm called chloroplastids, and these, in sunlight either 

 direct or diffused, have the power to manufacture the highly 

 complicated protein substance, chlorophyll. 



It is possible to extract chlorophyll in pure form from some 

 types of plants and to find out its chemical composition. From 

 such analyses it is known that the ordinary green chlorophyll is 

 a combination of green and yellow colored substances and that 

 the proportions of these determine the yellow, brown, or green 

 shade, while the reds are apparently due to the scarcity of nitro- 

 gen. If a beam of white light be passed through a prism it is 

 broken up into the seven primary colors of the spectrum. If a 

 similar beam is passed through a column of extracted chloro- 

 phyll it is similarly broken up, but some of the rays do not get 

 through, particularly those of the shorter wave lengths (blue 



