SYSTEMS OF TISSUES AND PLANT GROWTH. 



161 



S3 



CHAPTER III. 



SYSTEMS OF TISSUES AND PLANT GROWTH. 



409. The brief account of the cell and its modifica- 

 tions into tissues and ducts, prepares for the considera- 

 tion of the manner in which these organs are arranged 

 in the structure of plants. 



In the lowest groups of plant life the individual is 

 either a single cell or an assemblage of soft cells, with- 

 out special order of arrangement. 



410. Unicellular plants. The most simple forms 

 of plant life are single minute cells, called Bacteria, 

 the smallest objects that are 



known to exercise vital func- 



tions ; they are so small that 



50,000 laid on a line side 



by side would occupy a 



space less than an inch in 



length. The typical form 



is globular, appearing under 



the microscope as a minute 



granule or dot, as No. 1 in 



Fig. 511; they are, however, frequently elongated, and 



appear in an oval form, as in No. 2 ; again, they take 



on the form of a fine line, straight, curved, or crooked, 



as in No. 3 ; another time they are spiral, as in No. 4. 



These minute cells are stored with protoplasm, and 



swim in fluids from which they obtain nourishment. 



They increase by fission, and multiply with marvelous 



rapidity. They are found in the watery fluids of both 



animals and plants. 



Sarclne; 2 , Bacterium; 3i Vibro; 4 , gpiril . 

 lum> 



