A subsporangial vesicle is a vesicle which is below the sporangium on a fungus.
Is often used in the turgor-building and release to launch the sporangium from the stalk of the fungus using this spore-dispersal method.
e.g. The subsporangial vesicle in Pilobolus fills with fluid, thereby creating turgor pressure that is released, launching the sporangium out towards the light, with the intent of landing on a plant.
References
Subsporangial vesicle Wikipedia(Text) CC BY-SA