Bacteria in their Relation to Vegetable Tissue. 27 



afford a tolerably good substratum for the development of many 

 species of bacteria, and thus show that the tissues are not wanting 

 in the necessary nutritive materials, the conditions are different in 

 the struggle between the disease germ and the living plant. Unless 

 the germ is able to gain access to the inner tissues by means of acci- 

 dental lesions, it must force its way through the epidermal cell 

 walls, or the cell membranes of the interior tissue, either directly 

 from the outside, or after having first gained an entrance through 

 the stomata into the intercellular spaces. In either case it has no 

 supply of nutrient material with which to carry on its metabolic 

 activity, and is therefore unable to gain a foothold from which to 

 develop. 



If the bacteria could increase in sufficient numbers on the surface 

 of the plant they might be able to penetrate the tissues more easily. 

 That B. amylovorus is in this way able to gain access to the tender 

 tissues of the receptacle of the pear-flower is extremely probable. 

 The sugary secretions which are poured out by the nectariferous 

 glands in the flower induce insect visitation, and afford the best 

 possible medium for the growth of the bacilli which are brought to 

 it in the sticky exudate which adheres to the insect. Thus the 

 bacteria have a fertile soil prepared for their further development, 

 and are able to multiply with ease. Having thus secured such a 

 coigne of vantage, they are able to penetrate the non-cutinized tissues 

 beneath, and thus gain entrance to the inner parts of the plant. 



Do plant juices possess germicidal properties f 



Recent experiments in animal pathology have demonstrated that 

 the blood of many animals possesses the property of destroying 

 bacteria to a limited extent, either when brought directly in contact 

 with it in the body of the animal, or after it had been aseptically 

 removed. This bactericidal power of the blood enables the animal to 

 destroy, not only the saprophytic forms with which it comes in con- 

 tact, but also a certain number of even malignant bacteria, which 

 otherwise would be able to multiply in the body and finally produce 

 death. This line of investigation, so fruitful of results in immunity 

 in the animal kingdom, suggested a series of experiments as to 

 whether a corresponding condition might not exist in plant life as 

 well. 



Although we have in plant-tissue nothing homologous to the circu- 

 latory fluids of the animal body, it might be conceivable that the 



