248 Ellincrr Archer : 



walls of the vessels of the gummy substance directly it is formed 

 and so liievent further exudation, or in a solution which will 

 dissolve the exudation as fast at it enters the vessels. 



Various tests were att-empted to try and discover the solubility 

 of the blocking nuaterial, but without success. If the material 

 should be wound gum, which appears most likely, it ought to be 

 able to be detected by testing with phlorogluciii and hydrochloric 

 acid, with which it should give a bright red colour, but no colour 

 change was observable. A special stain for wound gum which 

 should stain it in contrast to the surrounding tissues known as 

 Hanstein's mixture, compo-sed of equal parts of concentrated alco- 

 holic solution of Fuschin and IMethyl Violet, a'lso gave no result. 



Xunierous tests for showing the presence of tannin were also 

 attempted, especially on sections of Acacias, but although the pre- 

 sence of extensive tannin was shown in the cortex, medullary rays, 

 and pith, tlie actual blocking substance in the vessels gave no defi- 

 nite tannin reaction. 



The exact nature of the substance exuded from the surrounding 

 cells into the vessels and causing blocking, therefore, remains 

 doubtful, although it is most probably a form of wound gum Avhich 

 will not react to the colour tests. 



Although the chemical nature of the substance exuded into the 

 vessels remains undiscoveied, an effective means was found of pre- 

 venting the blocking in Acacias. It was found that if fresh speci- 

 mens of Acacias, soon after being taken from the trees, are placed 

 in a dilute solution of the non-poisonous heavy metals, no blocking 

 occurs, and the flowers remain nearly perfect for a considerable 

 period. The metal Avhich proved most successful was lead, the 

 nitrate, and the acetate being the salts most used, as they are 

 the only two lead compounds easily soluble in water. Silver nitrate 

 in dilute solution also proved fairly effective, l>ut owing to its 

 power of rapid decomposition it is somewhat unsuitable. Soluble 

 mercury salts, presumably owing to their poisonotis properties, 

 proved i-apidly harmful, while the othei- members of the group 

 were not suitable for use. 



The following tables give some idea of the effect that immersion 

 of the stems in a weak solution of lead nitrate has on various 

 species of wattle. It would be diffieult to say exactly which day 

 a certain mass of wattle flower actually died, therefore in the fol- 

 lowing tables the condition of the flowers at intei'vals of two, six, 

 and fourteen davs was noted. In a good many cases the flowers- 



