THE LIVING WORLD 



199 



whence their name. That part of a mushroom, which 

 rises from the ground, is also a " spore " producer. 



The cells of plants are enclosed in a cell-wall which 

 consists of a substance known as cellulose, and which 

 contains no nitrogen. 



The unicellular water- weeds (algce) contain a green 

 substance termed chlorophyll, which somehow enables 

 them, during daylight, to dissolve carbonic acid and 

 retain its carbon, while they let its oxygen go free. 



FIG. 30. 



PORTIONS OF FIVE THREADS OF Conferva, 

 GREATLY MAGNIFIED. 



Showing the cells of which they are composed and also the protrusion 

 and blending of prominences of some of the cells, and the passage 

 of the protoplasmic cell-contents through two of the protrusions 

 which have blended. 



Such plants can, in this way, nourish themselves and 

 live on inorganic substances. Fungi, on the other hand, 

 which possess no chlorophyll, and are not green, cannot 

 do this, and therefore require for food living matter, or 

 matter which has lived. Both kinds of plants respire, 

 and therefore both, in breathing, take oxygen from the 

 air and give out into it carbonic acid from their own 

 substance in exchange, but it is only the green plants 



