Bacteria in their Relation to Vegetable Tissue. 17 



the weakened plant. To this latter class of phenomena it would 

 seem proper to limit the term immunity. 



We would scarcely consider the human body immune from the 

 attacks of ordinary saprophytes, even those forms which are normally 

 found in the oral cavity. Most of them seem to possess no ability to 

 thrive inside of the animal organism, but find their natural condi- 

 tions of existence in the dead organic material which is always 

 present in the mouth. Likewise, it would seem improper to say 

 that a rose is immune from Bac. tuberculosis because the tubercle 

 bacilli do not find in the tissues of the plant the necessary conditions 

 for their development. 



While the bacterial parasites already known are sufficient to indi- 

 cate that we cannot consider the vegetable kingdom as wholly free 

 from bacteria, yet we must admit that the susceptibility of plants 

 is very much less than that of animals. 



In considering, then, this exemption of plants from the attacks of 

 micro-organisms, we will divide the phenomena into two classes : 



First, those due to what may be called Resistance; second, those 

 due to Immunity. 



Before going farther, it will be necessary for us to determine the limi- 

 tations which will be imposed upon the meaning of these two terms. 



The inherent power of the vegetable organism to withstand the 

 action of bacteria in general may be termed Resistance. This resist- 

 ance which the plant offers to the entrance of micro-organisms may 

 be due to various causes, and is operative throughout the whole range 

 of plant life. It is the normal condition of the plant, and is closely 

 correlated with the conditions of nutrition, for when the natural play 

 of these forces is disturbed, and an abnormal state of affairs super- 

 venes, this power of resistance may be subject to greater or less modi- 

 fication. This lowering of the general vitality of the plant, due 

 possibly to a number of causes, is usually manifested in a lessening of 

 the powers of resistance which the plant seems to possess. The plant 

 organism becomes then more susceptible to the attacks of disease. 



This state of affairs must not be confounded with a condition 

 which affords a more favorable opportunity for the development of 

 the attacking parasite. The one concerns itself with those processes 

 which tend to lower the general vitality, and thus the resistance of 

 the plant ; the other relates only to those conditions which give 



