Cactus / seedling on seedling

I saw a person grafted a young seedling on a young stock in the website.
As my practical experience, I tried same method.
I grafted 12 seedlings for the 1st attempt. it seemed working well.
I grafted 12 more seedlings yesterday as the 2nd attempt.
The scion is a Pelecyphora aselliformis and the stock is a Cereus hybrid.
Both scion and stock seeds were sown on 19/08/2012.
The diameter of the scion is 2 mm.
The stock is held in a slit on a wet sponge rubber.