Silver Thiosulfate (STS) is used by professional breeders and is commonly used to block the action of ethylene in plant cell cultures.
Ethylene is a hormone that is present in the gaseous state. Ethylene increases during senescence and ripening,
and has been shown to increase in plant cell cultures in the presence of auxins.
Silver nitrate may be used alone to block the action of ethylene but it is not transported as well as STS.
Long but better description:
In a nutshell, almost all plants produce ethylene as they age. Apples and bannans are perfect examples.
Put an apple in with your bananas and your apples won't last very long. Nor will your bananas.
Ethylene is also responsible for forcing green bananas in a paper bag to ripen faster.
Food wholesale companies always gas a room full of green tomatoes or green bananas with ethylene to kick start the ripening process.
By the time they get to your grocers, they're almost ready to eat.
The Canabbis plant is Dioesious
, meaning it is either a Male or a Female plant. But never both (cough cough).
Tomatoe plants are Monoecious
, meaning they have both male and female sexual parts on one plant.
When a female is polinated by a male, both XX (female) and XY (male) chromosones are present.
If you spray a FEMALE cannabis plant with STS, the Ethylene the plant would normally make to ripen (and flower) is blocked.
With Ethylene blocked, the plant reverses to MALE and produces pollen sacs. Since the plant is FEMALE and no male has been introduce, only FEMALE chromosones are pressent.
This mean only female seeds are produced by the plant.
Neat Trick huh?