So there is always seed involved. Mutation has nothing to do with it. Only crossing two wild species will give more or less uniform offspring in the first generation. Chimaeral rearrangement can take place in the germline if the mutation is in chloroplast in a single cell. A nuclear mutation can only lead to a chimaera directly if happening at the stage that the organism already has two or more cells.
Meiotic recombination occurs during formation of pollen and egg cells with a high frequency.
So, if the parents are not homozygous, i.e. , have several genes in two different forms, this may lead to new combinations in the offspring due to segregation. A plant with the dominant yellow mutation will make pollen and egg cells with a gene for green or a gene for yellow. Mutation can also take place during seed formation but only with very low frequency. Although meristem culture is only an artificial way of vegetive propagation there are a few differences. In meristem culture the neat order of layers is easily disturbed.