Here is some info...
The properties of STS reported that its complex ions are more mobile and can be transported by the vascular system.
Perhaps this shows the difference between these stimulants.
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http://www.plantphysiol.org/content/83/1/44.full.pdf
The STS complex was used because 
it has much greater mobility in plant tissue than uncomplexed silver ion (16).
(16) VEEN H, SC VAN DE GEIJN 1978 Mobility and ionic form of silver as related to longevity of cut carnations. Planta 140: 92-96
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http://cuke.hort.ncsu.edu/cgc/cgc02/cgc2-9.html
While attempting to increase the longevity of cut carnations, Veen and  Van de Geijn (1) demonstrated the manifold mobility of the silver ion in  the anionic complex silver thiosulphate, [Ag(S203)2]3-, over that in  AgNO3. The anti-ethylene action of this compound prompted us to assay  its potential in sex reversion of gynoecious cucumbers. Initial trials  indicated that Ag(S203)2 induced male flowers much the same as AgNO3. A  more detailed experiment was carried out late in the fall of 1978.
(1)    Veen, H. and S. C. v.d. Geijn. 1978. Mobility and ionic form of  silver as related to longevity of cut carnations. Planta 140:93-96.
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http://ucce.ucdavis.edu/files/datastore/234-861.pdf 
The commercial application of silver as an antiethylene treatment was  made possible by the discovery by Veen and van de Geijn (1978) that the  silver thiosulfate (STS) complex was stable and 
highly mobile in the vascular system but was still very effective in preventing ethylene action.