| Brian, It is sometimes found that an F1 hybrid may express "pure" parental traits as mosaics -- the seed parent trait in some tissues, the corresponding pollen parent trait in adjacent tissues. For example, some blackberry-raspberry hybrids produce some fruit that are firmly attached to the core (like blackberries), some loose (like raspberries) and others that are partially attached (the "hybrid" condition). If the parents differ in trichomes or stomata, the parental types may segregate in adjacent tissues. Charles Naudin, the French hybridist, studied and wrote about this phenomenon in the 19th century, but Mendel -- who read Naudin's papers -- did not see it in his pea experiments. Or at least he did not discuss it. So, it is possible that your sport is of this type -- somatic segregation. Somatic segregation seems to include at least two distinct phenomena. One type may involve changes in gene activation. That is, a gene or chromosome segment is silenced in one parent, while the corresponding region is active in the other. If the silencing is copied to the active partner, the "sport" or mosaic region will tend to resemble the parent with the silenced segment. But if unsilencing is copied, the expressed trait will tend to resemble that of the other parent. The second type involves physical segregation resulting from somatic meiosis -- with or without spindle formation. Crudely stated, a cell may double its chromosomes in anticipation of mitosis, then "forget" to divide. If the cell was originally diploid, it will now be tetraploid and may continue as such for a mitosis or two. Then, it (or they) can "remember" and do an extra cell division to bring the chromosome number back to normal. Just like meiosis. I have an old report on this type of somatic segregation on a rabbit. It is possible to stimulate somatic segregation by feeding cells unpolymerized deoxyribonucleic acids or caffeine (which is easier to acquire). Apparently the cells are tricked by the free DNA (or caffeine) into "thinking" that chromosome duplication has already occurred, and slipping an extra cell division into their cycle. The haploid cells may then correct themselves by skipping the next cell division, which brings them back to their normal diploid condition. Here's a link to an article on caffeine and somatic meiosis in Arabidopsis thaliana. I think the caffeine trick should be used on sterile hybrids to obtain segregation without relying on flower formation. Caffeine could be introduced via an IV drip, if you can get the needle into the cambium. Or you might try Michurin's layering tube. Karl | 
