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Author Topic: Bulb Log 0313 Colchicum corms  (Read 1372 times)

Ian Y

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Bulb Log 0313 Colchicum corms
« on: January 21, 2013, 02:00:16 PM »
My describing Colchicums as bulbs in my Bulb Log last week has stirred a fascinating discussion – just what I love - because most authorities call it a corm. A few people have kindly been in touch to point out my mistake. Jim McKenney puts a very strong case in his posting on the PBS discussion list which I copy below.

http://www.pacificbulbsociety.org/


Bulbs,corms and tubers
Jim McKenney (Thu, 17 Jan 2013 12:23:39 PST)

No other source that I’m aware of, even the wonderful PBS
wiki, speaks to my inner bulbist with the authenticity and congeniality of
Ian’s bulb log.  Over and over Ian has
intuitively published just the images and discussions I want to see to nurture my bulb
enthusiasm.

But I do have one quibble about his posting on bulbs and
corms. While I was glad to see Ian finally settle into the “erythroniums as
bulbs” camp, I was disappointed to see him place colchicums in the bulb camp. Let’s
see if I can persuade him to rejoin the “colchicums as corms” camp.
Ian proposed the hypothesis that the colchicum “bulb” is a
single-scale bulb. “Scale” in these contexts usually refers to a modified leaf.  He included a pair of images, one of a
colchicum and one of a group of tulips, which call attention to the seeming
similarity of the two : in each case, the image shows a bulb or bulbs with a
sprout or a stem emerging or attached. At first glance, they certainly do look
alike.

But give consideration to what is shown: in the case of the
colchicum, one sees a living sprout emerging from the base of the “bulb” inside  the tunic.  In the case of the tulips, one sees dead
annual stems attached to the exterior of the dormant bulbs (i.e. outside the
tunic). In the case of the colchicum, the structure which is emerging is mostly
the true, perennial stem of the corm, a stem whose distal portion will later
differentiate into annual stem, leaves and maybe flowers and fruit. I believe that the solid
mass which forms at the base of this structure is stem tissue, not leaf tissue.
It’s thus a corm, not a bulb.

The structures shown in the images are not truly homologous
structures: the dried stems of the tulips correspond only to the structures
which will eventually develop at the distal tip of the colchicum sprouts (the
basal part persisting as the corm).

Medieval botanists gave colchicum the mistaken sobriquet “filius
ante patrem” (i.e. the father before the son, because seeds appeared in spring
but flowers did not appear until fall).  Ian’s
images similarly confuse the chronology of things: the dry stems attached to
the tulip bulbs are the previous year’s annual stems, whereas the sprout on the
colchicum are of the current season. 

If someone can cite a study of the embryogeny of these
structures in colchicum which demonstrates that the tissues in question are
leaf tissues, then I’m ready to join Ian in the “colchicums as bulbs” camp.  Until then, I’ll be glad to welcome him back into
the corm camp.



I have always been the type of person that questions everything and is never fully convinced until I have worked it all out for myself and yes Jim I am very tempted into the corm camp.

Most authorities classify Colchicum as a corm and on checking back I have described it as both a corm and a bulb – showing I cannot make my mind up conclusively. I apologise for causing this confusion but it does show the difficulty we growers can have in knowing what we should be calling these structures – using term bulb in its non-botanical context is best.

I have attached some more pictures showing the early growth stage of the emerging shoot which to me seems to be rising from a ‘basal plate’ at the side and base of the storage structure - the large storage structure also sits on the base.

Jim I am happy to join you in the corm camp but I still have a niggling question and am still trying work out for my own sake precisely what is going on and whether this structure is made of stem tissue or leaf tissue. This year I will try and conduct more inspections through the growth stages of Colchicums to try and understand exactly what is happening so I can be persuaded.

As Jim states if someone has done the embryogeny I too would like to see it so I can move 100% into the corm camp.

Jim’s point on the tulip is well made and I accept that fully.

My parents and Teachers would confirm that I was always the student that questioned everything, had to work it out for myself and was never willing to take things for granted.

This discussion is just one of the fascinations that bulbs hold for me....

 

« Last Edit: January 21, 2013, 02:04:34 PM by Ian Y »
Ian Young, Aberdeen North East Scotland   - 
The person who says it cannot be done should not interrupt the person doing it.
http://www.srgc.org.uk/bulblog/bulblog.html

 


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