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Re: Hosta Buds (I)


> 
> Robins,
> 
> My discussion of "Hosta Buds" continues with the assumption that we are
> talking about buds which occur throughtout the year. Thus, there are
> dormant buds and buds that are NOT dormant. Dormancy was discussed in
> some detail in "Hosta Dormancy Redux" in The Hosta Journal (see Vol. 26,
> No. 1, pg. 33). From reading this article you are reminded that dormant
> buds result from either water stress in late summer or from cold weather
> which begins in the fall. Dormant buds occur as a result of the growth
> of bud scales around meristematic tissue of the axillary buds on the
> upper sides (in the axils) of each leaf petiole. Leaf scales are
> encouraged (promoted)  to grow by the accumulation of Abscisic Acid
> (ABA), a naturally produced hormones in leaves, petioles and roots of
> the plants. Simultaneously, meristems are discouraged (inhibited) from
> growing by the same level of ABA hormone. This is quite typical of some
> plant hormones...i.e. a given concentration may promote growth of cells
> in one tissue but inhibit growth of cells in nearby tissue. Dormant buds
> occur only in late summer and during fall and winter months. They are
> the product of the presence of ABA. This, then, is the criterion for
> determining if buds are dormant buds.
> 
> So, what about buds in axils of petioles that do not grow for some
> reason? Are  they not dormant buds? IMHO, they are buds that are
> inhibited from growing because of the presence of other hormones
> (auxins) being produced by growing tips and leaves. These auxins have
> been studied in many plants  by hundreds of plant physiologists over
> many years. While I doubt that many studies have been conducted in
> Hostas specifically, I do not think that different general findings
> would occur which differ from those of other Genera. Auxins, which occur
> naturally in all higher plant life, have been  found by analysis to be
> Indoleacetic Acid (IAA), responsible for many growth responses in plants
> including callus formation, rooting, tropisms, cell growth, apical
> dominance  and many other phenomena.
> 
> I suggest that readers may wish to take an inexpensive hosta division,
> take it apart leaf by leaf starting at the top. Leaves are opposite each
> other about 180 degrees. In the axil of each leaf is a small bud. The
> size of the buds decrease  within the whorl of buds on the rhizome in a
> decending fashion. When the plant is very small, such buds are difficult
> to find but they are in place, not growing, because of the inhibiting
> effect of hormones being produced by leaves and growing shoots that have
> growing tips producing significant quantities of auxins. These hormones
> move downward, not by gravity but by physiological means called polarity
> which are not fully understood. As auxins accumulate they inhibit growth
> of the small buds. As soon as the level of production is reduced (such
> as when a tip is destroyed or when a flower scape develops from the
> previous vegetative growing tip), then growth of buds which were not
> growing previously , may commence. They may grow, compete with other
> buds, and may become dominant over others.
> 
> To call all buds which are not growing "dormant buds" is an error. Nor
> are they "resting". I would characterize them as "being arrested", not
> yet growing or prevented from growing. I suggest we call such buds that
> we find in the spring and summer "dominated buds" or "recessive buds".
> That is what they are. They have been dominated by other buds or are
> recessive to other, more competitive buds which are producing more
> auxin-like hormones.
> 
> All of this may sound like semantics to some readers. I can assure you
> that just winning an argument over words is not my objective. I really
> don't care what one calls them, but the use of accurate nomenclature and
> proper use of the English language is the best method to make certain
> that one understands the proper morphological structures and
> physiological functions of the various plants organs, tissues, cells and
> their constituent components. I have tried to make this discussion as
> simple as possible. It is based upon known information that anyone can
> find in a good Botany text book. I have tried to be logical in
> interpreting and presenting  this information in an objective way. I
> hope it has been helpful.
> 
> Jim Hawes Oakland MD
> hawesj@gcnet.net

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