248 Ellinov Archer : 



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

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

 dissolve the exudation as fast at it enters the vessels. 



Various tests were attempted to try and discover the solubility 

 of the blocking material, 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 phloroglucin 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, composed of equal parts of concentrated alco- 

 holic solution of Fuschin and Methyl Violet, also gave no result. 



Numerous 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, the 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 which 

 will not react to the colour tests. 



Although the chemical nature of the substance exuded into the 

 vessels remains undiscovered, 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 which 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, but owing to its 

 poAver of rapid decomposition it is somewhat unsuitable. Soluble 

 mercury salts, presumably owing to their poisonous properties, 

 proved rapidly harmful, while the other 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 difficult 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 intervals of two, six, 

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



