I have been taking care of an hibiscus plant that was donated to the library where I work . It's been healthy and blooming all winter , but now it's exhibiting a sticky subtance beneath it's leaves ......and has stopped blooming . There are little droplet-like mounds of this substance hanging on the spines of the leaves . I see no bugs of any kind . I'm a janitor and know nothing much about plants , but i've grown rather fond of this particular plant . Any advice would be greatly appreciated . Thanks !