david walker david at alegba.demon.co.uk
Sun Feb 13 10:36:33 EST 2000

Re detecting CAM in Kalanchoe leaves by acidity


In 1813 Benjamin Heyne wrote this to the UK Linnean Society

Dear Sir,
I had an opportunity some time ago of mentioning to you a remarkable,
deoxidation of the leaves of a plant in day-light. As the circumstance is in
itself curious, and throws great light on the opinion of those celebrated
philosophers who have written on the subject, I will state it shortly in
this letter, which if you please, you may in extract, or in any other way
you think proper, lay before the Society. The leaves of the Cotyledon
calycina, the plant called by Mr. Salisbury Bryophyllum calycinum, which on
the whole have an herbaceous taste, are in the morning as acid as sorrel, if
not more so. As the day advances, they lose their acidity, and are tasteless
about noon; and become almost bitterish towards evening. This is the case in
India, where this plant is pretty generally cultivated in our gardens and it
remains to be seen if the same takes place in the hot-houses in England,
where it has been lately introduced.


Some time in the 60s, I was asked to give a University of London lecture.
This was an awesome task for a shy young man because London University
lectures (as opposed to lectures in one of the many constituent colleges of
the university) were infrequent events which drew audiences of students who
were more or less blackmailed into going by promise of an examination
question on the lecture topic. Wishing to lighten the occasion a little i
decided to repeat this historic observation. Relying on my past association
with the University of Newcastle, where much of the pioneering work on Cam
was done by Thomas and his colleagues, I begged a hundred Kalanchoe crenata
leaves, illuminated half and kept the other half in the dark. The acidified
leaves were left with long petioles the deacidified leaves with short. The
aydience was asked to decide which was which on the basis of taste.
Kalanchoe leaves taste awful in any circumstances but the audience rose to
the occasion amid cries of anquish and finally cheers of enthusiasm when I
pulled into sight a blackboard which showed that they had got it right by
about 95 to 5.


Forgive the advert but you can find all of the old CAM stuff in Energy
Plants and Man (http://www.asu.edu./clas/photosyn/books/walkerbk.html) which
Amazon stock even if your library doesn't!

David Walker



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