what is considered bulbous

Agoston Janos agoston.janos@citromail.hu
Fri, 25 May 2007 05:52:47 PDT
Dear Jim,

You are right. But I also have to add, that we also cannot say that only tender plants can be bulbous. Iris ochroleuca subsp. gigantea has hot here a kind of woody rhizome. It is actually not like a wooden stem (tree), but it is very hard to divide. If i can finally broke a rhizome, the surfaces look like as the surface of a broken brach, just a bit more fleshy.

And yes, there are also many transitions...

----- Original Message ----- 
  From: Jim McKenney 
  To: 'Pacific Bulb Society' 
  Sent: Friday, May 25, 2007 1:52 PM
  Subject: Re: [pbs] what is considered bulbous

  We've had several postings on the topic of "what is a bulb" lately, and this
  most recent one by David Ryle prompts me to jump into the fray.

  I'm by no means rigid about this: fitting an a-priory concept such as "bulb"
  to the happenings in the real world always seems to involve a bit of

  David Ryle wrote: "All plants that grow from what would commonly be thought
  of as a bulb etc; 
  are known botanically as geophytes. By definition a geophyte is a plant that

  grows from a modified leaf that has evolved into a storage organ."

  David gives us a definition; definitions by their nature are neither right
  nor wrong, they're just definitions. To the extent that they work, we use

  But the one he gives does not work for me. 

  To say that "a geophyte is a plant that grows from a modified leaf that has
  evolved into a storage organ" is to approximate the traditional,
  conservative definition of "bulb", but it does so to the exclusion of many
  other geophytes such as those which grow from corms or other stem tissues. 

  It is the bulb (in the narrow sense) which has as a primary storage tissue
  modified leaves. The scales of a lily, for instance, are modified leaves.
  The major food storage parts of a tulip bulb are modified leaves.

  Crocuses are geophytes, but they do not have modified leaves as their major
  storage tissue; their major storage tissue is stem tissue. 

  Since the one thing all geophytes that I know have is stem tissue in one
  form or another, I think it makes sense to set up a definition where the
  role of stem tissue is central. 

  A bulb, in a sense, is a corm supplemented with storage tissue in the form
  of modified leaves. I think of bulbs such as lily bulbs or tulip bulbs as a
  corm (the so-called basal plate, which I prefer to call the perennial stem)
  surrounded by modified leaves which serve as storage tissue. 

  Since the plants which form bulbs, corms and so on are not always related
  (the majority are monocots, but some are dicots only very remotely related
  to the monocot bulbs), it should not surprise us that the observed
  structures do not fall into neat categories.

  For instance, what should we call the structure from which Achimenes grow? I
  think of it as an elongated basal plate surrounded by modified storage
  leaves, superficially similar to the underground parts of some native North
  American lilies. I'm pretty much alone in calling the Achimenes structure a
  bulb, but even those who insist that that structure cannot be a bulb will
  call the similar structure in the lilies a bulb. 

  One might say that if the primary storage tissue is leaf-derived, then it is
  a bulb. If the primary storage tissue is stem derived, then it is something
  else. I've never had the patience to remove all the little modified leaves
  from an Achimenes bulb to weigh them and then compare that weight to that of
  the structure to which they were attached. But you get the idea. Since
  Achimenes are gesneriads, we should not be surprised that it is difficult to
  fit them into a scheme originally devised to describe the storage structures
  of liliaceous plants.

  When I look at plants like Echeveria, Sempervivum and such I can't help
  seeing the gross similarity to bulbs like lily bulbs. There is, in fact, a
  purportedly epiphytic lily species named Lilium sempervivoides. 

  Another intermediate condition is seen in Florence fennel, a cultivated form
  of fennel in which the base of the petiole is swollen to form, with the
  petioles of other leaves,  a bulb-like structure. This "bulb" grows
  partially buried, partially exposed. Is it a geophyte? Does a bulb have to
  be a geophyte? Can an epiphyte such as the lily mentioned above be a

  It seems to me that we can't be too strict about any of this: there are too
  many intermediate forms to allow definitions which are both tight and
  workable. Also, in the discussion above the emphasis is on structure. But
  surely life cycle should enter into any definition of geophyte. The
  structure of a Sempervivum might suggest a bulb to some, but the life cycle
  of a Sempervivum certainly doesn't. Florence fennel does not have an
  underground dormant phase - bulb or not, it's hardly a conventional

  I think we need to keep some wiggle room in our concepts. 

  Jim McKenney
  Montgomery County, Maryland, USA, USDA zone 7, where I've been hand
  pollinating - apparently successfully -  the big pink Eremurus to get seed.

  My Virtual Maryland Garden http://www.jimmckenney.com/
  Webmaster Potomac Valley Chapter, NARGS 
  Editor PVC Bulletin http://www.pvcnargs.org/ 
  Webmaster Potomac Lily Society http://www.potomaclilysociety.org/

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