This usually happens to me outdtoors when some unknown but genetically close species drops some pollen on your pistils, and the plant reacts weird, but can be passed on genetically . i found this for you since i like your expirements 
Polyploidism
Polyploids are individual organisms that possess double the normal amount of chromosomes for the species they belong to. Occasionally, this trait can be fixed into plant species via breeding programs—for example, durum wheat (used to make pasta) is a polyploid form of wheat created via an inter-species cross of two grasses with the typical chromosome count.
In cannabis, rare instances of spontaneous polyploidism can occur if the normal process of cell division malfunctions during development, and can be also be induced in plants that would otherwise develop normally by treatment with a powerful chemical called colchicine.
Polyploidism is considered useful, as it is thought to cause a significant increase in THC production, as well as gigantism (extra large plants with extra large buds!). Up to now, it appears that no true-breeding strains have been developed, although rumours on internet forums suggest that at least one breeder is attempting it. passing the love~~!