PRACTICAL COURSE IN BOTANY 



Fig. 10. — Transverse section near the 

 outside of a wheat grain : e, the husk ; a, cells 

 containing protein granules ; s, starch cells 

 {after Tschirch). 



4. Organic foods. — These four substances, starch, sugar, 

 fats, and proteins, with some others of less frequent oc- 

 currence, are called organic 

 foods, because they are pro- 

 duced, in a state of nature, 

 only through the action of 

 organized living bodies, or, 

 more strictly speaking, of 

 living vegetable bodies. 



5. Our dependence upon 

 plants. — ^ While the animal 

 organism can digest and 

 assimilate these substances 

 after they have been formed 

 by plants, it has no power 

 to manufacture them for 

 itself, and, so far as we know at present, is wholly depend- 

 ent upon the vegetable world for these necessaries of life. 

 In one sense the whole animal kingdom may be said to be 

 parasitic on plants. The wolf that eats a lamb is getting 

 his food indirectly from the grains and grasses consumed 

 by its victim, and the lion that devours the wolf that ate 

 the lamb is only one step further removed from a vegetable 

 diet. 



6. The vegetable cell. — If you will break open a well- 

 soaked horse bean and examine the contents with a lens, you 

 will see that they are composed of small oval or roundish 

 granules packed together like stones in a piece of masonry. 

 These little bodies, called cells, are the ultimate units out 

 of which all animal and vegetable structures are built up, as 

 a wall is built of bricks and stones. They differ very much 

 from bricks and stones, however, in that they are, or have 

 been, living structures with their periods of growth, activity, 

 decline, and death, just like other living matter, as will be 

 seen by and by, when we come to look more particularly 

 into their life history. They consist usually of an inclos- 



