last week i return in Villa Taranto(Pallanza ,Verbenia ,Italy) i see the very big acer pictum Usugumo and wow ! some branch have a little " black bag" ,i ask to garden man the reply is :this bag are for propagation acer pictum Usugumo in the bag there are sand and "torba"(acid soil),the branch is two years old,water by syringe, cut a little the bark of the branch, before to tie the black bag;and after one year cut and the new acer are ready!!