34 



FUNDAMENTALS OF AGRICULTURE. 



SECTION VII. KINDS OF PLANTS. 



Number of Plants. Perhaps between 200,000 and 

 250,000 different species of plants are already known, 

 and it has been estimated that possibly as many more 

 really exist but are as yet unknown. Of the known 

 plants, about one-half are called seed plants, while the 

 remainder comprise the ferns, mosses, algae, fungi, 

 and bacteria. 



Bacteria are perhaps the simplest plants known. 

 They consist usually of but one cell each, or a few 



I. Typical rod-shaped bacteria. 2. Bacteria with hair-like appendages which enable 

 them to swim in milk or water. 



such loosely connected. They are all microscopic in 

 size, rarely exceeding one five-thousandth of an inch 

 in length and sometimes not one-tenth as large. They 

 are visible to the naked eye only when they occur in 

 immense numbers, as slimy masses. They do not 

 (with few exceptions) make their own food, but are 

 either parasites or saprophytes. They multiply rap- 

 idly by simply growing in length and dividing in the 

 middle. Under favorable conditions, this may occur 

 every twenty minutes, so that in ten hours, if nothing 

 hinders their multiplication, one germ would give rise 



