Pulling down to correct level

Jim McKenney jimmckenney@starpower.net
Tue, 12 Jul 2005 19:51:10 PDT
Alberto, I respectfully and vigorously disagree with your statement that
true bulbs are never renewed. 

Yes, there are many true bulbs (especially members of the Amaryllidaceae)
which seem to persist indefinitely.  

Whether or not that is true or not depends on how one defines bulb. 

When I say bulb, I mean that structure which consists of a basal plate, an
embryonic sprout/bud, and  the attached storage scales (which are modified
leaves) surrounding the bud. 

Of those three basic elements, only part of the basal plate persists from
year to year. The sprout is always of annual duration in north temperate
bulbs and its surrounding storage scales are generally of annual duration.

That's why I said that the tulip bulb you plant in the fall is not the same
one you dig in the summer: of the three basic elements described above, only
some the basal plate persists from year to year. Most of the tissue which
made up the bulb which you planted is gone at the end of the growing season.

With amaryllids, it's not so obvious, but the bulb (bud + scales + basal
plate) is not persistent. It is constantly being replaced by another bulb
(or several bulbs). Because the new bulb forms inside the old one, it
superficially looks as if the original bulb persists. 

The sprout on all bulbs I know sprouts only once. After that, it is replaced
by another sprout on the same basal plate. That new sprout has its own
surrounding storage scales, sometimes supplemented by scales surviving from
the old bulb. But the sprout is always a new one. And as the old sprout
dies, the axis of annual growth shifts to the axis of the new sprout. And
around that axis are arrayed the elements which make up the new bulb. 

From the outside, it looks like the same old bulb. But on the inside, the
old bulb has disappeared and been replaced by a new one. 

Jim McKenney
Montgomery County, Maryland, USA, USDA zone 7, where I've been sitting here
typing for so long that I'm beginning to think of my bottom as my basal

-----Original Message-----
From: pbs-bounces@lists.ibiblio.org [mailto:pbs-bounces@lists.ibiblio.org]
On Behalf Of Alberto Castillo
Sent: Tuesday, July 12, 2005 10:14 PM
To: pbs@lists.ibiblio.org
Subject: Re: [pbs] Pulling down to correct level

    But Jim, true bulbs are NOT renewed every year, in fact they are never 
renewed. Those in most families will only grow fatter each year until they 
    It is corms that are renewed during each growing season (with very few 
exceptions, like Ferraria).
All the best

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