180 PLANT PHYSIOLOGY 



to Treub's theory of protein formation has been previously men- 

 tioned. 



4. In the base of extrafloral nectaries as well as in the surround- 

 ing tissue, are commonly present glucosides, which may play a 

 part in the secretory action of the nectaries. 



5. Easily oxidizable materials such as aldehydes and acids may 

 be protected against too rapid or premature oxidation by being 

 transformed into glucosides. This has been given as an explana- 

 tion of the aldehyde and acid glucosides. 



6. Many anaesthetics like ether and chloroform have a marked 

 effect upon growth (Chap. XXVI), behaving like a stimulant, 

 and in many cases the rapid growth which results is accompanied 

 by the hydrolysis of glucosides present. It has been suggested 

 that the rapid growth is due to a stimulus provided by some 

 component of the glucoside, or that the glucoside contains one of 

 the plant stimulants to which the name hormone has been given 

 (Chap. XVII). This occurrence of glucosides in rapidly growing 

 tissues was mentioned above (2), but according to the concep- 

 tion there presented the presence of the glucosides was explained 

 in an entirely different way. 



7. The bitter taste and poisonous nature of many glucosides 

 may serve as a protection against herbivorous and fructivorous 

 animals. In seeds, leaves, and bark such protection would be 

 very helpful, and there is no doubt that the presence of such sub- 

 stances does render the parts which contain them less attractive. 



8. Many of the nonsugar elements of glucosides are bacteri- 

 cidal and prevent the growth of fungi and bacteria. Their presence 

 in bark provides a naturally antiseptic condition, which may be 

 useful to the plant in case of wounds, and it may well be that one 

 of the reasons why the processes of decay do not easily set in until 

 the cell is dead, is because of the presence of these antiseptic gluco- 

 sides. It is interesting to recall in this connection that the gluco- 

 side is not normally hydrolyzed in leaves, seeds, etc., until the 

 tissue is wounded or cut. This permits the enzyme to react on the 

 glucoside with the production of the toxic or antiseptic compounds. 



Organic Acids. — Aside from the organic acids associated with 

 the fats, other acids are often present in the cells of plant tissues, 

 where they are formed by the incomplete oxidation of carbohy- 

 drates under certain, special conditions. Among those not pre- 

 viously mentioned are acetic, malic, oxalic, tartaric, and citric acids. 



