| Abstract: | Stems of Pyrus calleryana, P. ussuriensis and P. communis var. jaspoideae, from both current and previous year's growth, were sampled in January and March and the phenols in the bud, cork, green cortex, white phloem and xylem tissues were investigated. For the individual tissues there appeared to be very little difference between the phenols of current and previous year's growth. However, although some phenols, such as arbutin and vanilloylcalleryanin, occur throughout all tissues of both January and March stems at about the same concentrations, certain other phenols tend to accumulate in particular tissues at particular times. The flavonoid glycosides, for example, were found in the buds, cork and green cortex, generally at markedly lower levels than in the leaves, but were absent from the white phloem and xylem. A comparison between leaf and whole bark (i.e. cork + green cortex + white phloem) of all available Pyrus species has shown that the bark phenols are generally more restricted in range than the leaf phenols and that no new phenols, hitherto undetected in the leaf, are to be found in the bark. Caffeoylcalleryanin and catechins are more obvious as bark rather than leaf constituents; as a leaf constituent, caffeoylcalleryanin has a somewhat limited distribution within Pyrus but as a bark constituent it is almost ubiquitous. |
