118 MASSACHUSETTS HORTICULTURAL SOCIETY. 



is also very simple. When a bacterium has reached maturity it 

 divides by a constriction at the middle into two individuals. Thus 

 in reproduction is the parent plant ever effaced yet always perpet- 

 uated in its offspring, since each offspring is a half of the parent. 

 Under ideal C()nditions of food, moisture, and temperature multipli- 

 cation is amazingly rapid. Some bacteria will mature and divide 

 in half an hour. It has been estimated that under ideal conditions 

 a single bacterium would in two days produce no less than 281,500,- 

 000,000 descendants, or a bulk of one pint. While this could 

 never actually happen in nature on account of the limitations of 

 food and the accumulation of their own injurious excretions, still 

 it gives us some faint notion of the unlimited power of increase that 

 these minute organisms have and will help us to appreciate how 

 the havoc wrought by some of them in our cultivated crops is pos- 

 sible. Many bacteria have long thread-like flagella, organs of 

 locomotion, by the lashing of which they are able to propel them- 

 selves through the liquids in which they live. This is very generally 

 true of those that cause diseases of plants. In order to take in 

 food bacteria must be immersed in it. The food must be in solu- 

 tion in water; it must be soluble. It soaks through the enclosing 

 membrane to the protoplasm within. In other words it is absorbed. 

 The food of bacteria is usually the highly organized materials of 

 other plants and animals. The great activity with which bacteria 

 increase is largely due to the fact that these complex food materials 

 are readily absorbed and converted into living protoplasm. The 

 absorption of food and the consequent growth are accompanied 

 by the excretion of certain poisonous substances by the bacteria. 

 When produced in sufficient quantities these poisons become detri- 

 mental to the bacteria themselves, stopping their growth and multi- 

 plication. In the case of disease-producing bacteria it is these 

 harmful excretions that are largely responsible for the injurious 

 effects on the host. 



While it is true that certain bacteria are detrimental to the general 

 welfare of mankind by far the great majority are harmless or 

 directly beneficial and necessary to our life and modern civilization. 

 It is well to recall that many of the industrial arts and commercial 

 processes such as the "retting" or maceration of linen fiber and 

 hemp, the manufacture of vinegar, the production of indigo, the 



