68 



ELEMENTARY BOTANY. 



Epidermis 



adjacent ones. By this continuity of protoplasm an intimate 

 union of all parts of the individual plant is established. 



9. The cells in the very early development of the plant, 

 and those in simple plants, are nearly or quite alike. Later 

 they may take on different shapes and functions. Several 

 kinds of tissue can then be recognized. In our common her- 

 baceous and woody plants there may be found three distinct 

 systems, namely, the epidervial, the woody strands, and the 

 fundamental tissue. The first of these includes the epider- 

 mis, the hairs and scales, and the stomates. The epider- 

 mis (Fig. 101) is the external compact layer of cells, pro- 

 tecting the more delicate tissue 

 below. Outgrowths of the epi- 

 dermal cells form hairs. These 

 may be one-celled or they may 

 become several-celled ; they may 

 be simple or become branched ; 

 sometimes they are glandular at 

 the tip. The general function 

 of the hairs is to protect the 



parts on which they grow, but in special cases they have other 

 duties to perform ; for example, the rhizoids (root-hairs) absorb 

 food from the soil. Scales are composed of many cells, and 

 like the hairs, they represent modified epidermal cells. 



10. The stomates are very small openings through the epi- 

 dermis. They are popularly spoken of as " breathing pores," 

 since the oxygen, as well as other gases, passes through them. 

 One of their very important functions is to convey from tlie 

 interior of the leaf the excessive amount of moisture which 

 the roots absorb in taking up the necessary mineral matter for 

 food. Examination with the microscope shows that the sto- 

 mate is an opening between two cells, which are called guard- 

 cells. These are very different in outline from the other epi- 

 dermal cells. Each is nearly Iialf-moon shaped, the two joined 

 together being broadly oval or spherical (Fig. 10'2). They con- 

 tain chlorophyll, which is not usually present in the other epi- 

 dermal cells. In section also they appear different from the 



Pig. 101. 



