THE ORGANIZATION OF THE PLANT 57 



means " seed plant," and this name was given to the highest 

 group of plants in recognition of the way in which they are 

 reproduced. All the other groups are developed from tiny 

 one-celled structures called spores. These are individually 

 too small to be seen with the unaided eye, but in masses are 

 recognized as the black mold on bread, the smoke from puff- 

 balls, and the like. 



The regions of the plant. A typical flowering plant is 

 often said to consist of root and shoot. The stem, however, 

 is the real axis of the plant and bears all the other organs. It 

 is present in the seed, and the first root grows from it ; in- 

 deed, roots normally grow from stems, not stems from roots, 

 as is popularly supposed. The root grows downward in the 

 soil, holding the plant in place and absorbing necessary mois- 

 ture and minerals. The shoot pushes up into the air from 

 which it takes other necessary food material. In the leaves 

 and other green parts of the plant these materials from both 

 the earth and air are ultimately combined to form plant food 

 by means of energy derived from sunlight. After a store of 

 plant food is secured, flowers appear, and seeds are formed 

 for the purpose of reproducing, multiplying, and distributing 

 the species. These two functions, growth and reproduction, 

 are common to all plants. During the early part of their 

 existence the growth processes are in the ascendant ; later, 

 reproductive functions prevail. 



Cellular structure of the plant. All parts of the plant are 

 formed of minute boxlike structures called cells-, which are 

 usually much too small to be seen without the aid of the mi- 

 croscope. The ordinary undifferentiated cell consists of a semi- 

 fluid, nearly transparent substance called protoplasm surrounded 

 by a thin membrane known as the cell wall. Within the proto- 

 plasm are one or more spaces called vacuoles containing a 

 watery fluid, the cell sap. Somewhere in the protoplasm, also, 

 usually at one side of the cell, is a denser, darker part called 



