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sucking its own paws —there would soon be nothing but bacteria left 

 to feed upon one another In our own bodies we hava the white blo^d- 

 corpuscles whose function it is to destroy any bacteria that may find 

 an entrance into the blood. In some diseases infected spots are shut 

 off from the rest of the body by layers of resistant tissue that keep 

 the " germs" from getting into the general circu'ation, and in time 

 causes their destruction from lack of food. I'lants ilo not have white 

 corpuscles, but it is certain that they have s )me means of resisting 

 such attacks. 



Perhaps the simplest way of keeping out bacteria would be the dry- 

 ing of the tissues ai'ound the wound, and we find that this takes place 

 frequently. The hard, dry cell walls do not easily j^ield nourishment 

 to the "germs," as we know from the length of time seasoned timber 

 lasts. Cellulose, which is the principal constituent of the cell walls, is 

 closely related to sugar, starch, glucose and a number of gums, but it 

 is much more resistant to the action of chemicals, and digestive fluids 

 d t not readily dissolve it. When the wood is fresh th-^re is a greater 

 chance that the cellulose may be eaten awav. After drying it resists 

 the attacks long enough to give the plant an opportunity to strengthen 

 its defences. Among many cryptogaraous plants this is the sole 

 method of protection, while only a few phanerogams depend on it alone 

 As a rule, they produce a layer of " woun'l-cork" that cuts off the injured 

 spot from the underlying parts of the stein. This is nearly a complete 

 cure in the case of the more tender parts. Woody stems form a '"cal- 

 lus" by the growth of the surrounding cells that afterwards form a 

 cork}^ layer. The new wood gradually spreads over the wound utitil 

 the edges meet and coalesce. Outwardly it seems as if there had been 

 no harm done, but the injured cells inside remain brown and dead, and 

 can be seen until the decay of the tree, by cutting into the wood. 



When a thin section of the " wound-wood" is examine 1 under the 

 microscope it is seen to be made up of nearly cubical cells that are 

 quite unlike the usual elongated cells of normal wood. As the tree 

 increases in diameter these wound cells become more and more like 

 those of injured wood. 



Many plants possess strongl3'^-smelling " ethereal oils" that pi ly a 

 part in warding off enemies that might otherwise use them for food. 

 These substances are often contained in special glands or receptacles. 

 The different gums and resins occur in similar canals and receptacles 

 throughout the plant. One of their principal uses seems to be to flow 

 out and cover up wounds, and in this way to prevent the entrance of 

 injurious fungi or bacteria. Cherry tree gum is familiar to all, and 

 the resin on pines and the related trees will keep away almost any- 

 thing, including bacteria, but a small boy with climbing proclivities. 



Most of the information here given was obtained from Strasburger's 

 " Lehrbuch der Botanik," but the subject was suggested by seeing 

 some peculiar lumps on the trunks of the beeches. There seemed to 

 be no especial reason for their presence until it was noticed that nearly 

 every one had either a dead t^ig protruding frjm it or showed some 

 sign to indicate that one had been there. It is evident that a dead 

 branch is in realitj^ a serious kind of a wound, for the decaying wood 

 is in such close connection with the main stem that there is gr ^at dan- 

 ger of the infection being communicated to the whole plant. When 



