Raphides ('stinging cells') in Aroids.

From: "Julius Boos" ju-bo at msn.com> on 2002.07.15 at 00:59:24(9108) Dear Fellow Aroiders, I am directing this note mainly to researchers who may have knowledge on the mechanism of the raphides said to occur as a protective ( ? ) device in Aroids, perhaps some of the European members may have some information that they may post to this list?? The 'story' is as follows---there are illus. in Deni Bown`s books on Aroids pg. 279 in the second edition) showing what are said to be the specialized structures called 'idioblasts' that 'expel the raphides that harm tissue when any Dieffenbachia and some of the other aroid genera) are damaged. This illus. is based on photos published in an old issues Aroideana (Middendorf, E. 1982. The remarkable shooting idioblasts. Aroideana 6 (1): 9-11.). The problem is that with a good microscope Ted Held +More >Ted.Held@hstna.com< has been unable to re-locate these structures! After lots of experimentation with many methods of extraction he has located and photographed some needle-like structures, but thus far nothing that looks like these said-to-be 'special ejector cells' or idioblasts. Ted also questions the ability of these structures to eject the needle-like raphides they contain in the manner described. There is also an article by Peter Boyce (Boyce, P. C. 1993b. A possible defense mechanism Scindapsus latifolius (Araceae: Monsteroideae). Aroideana 16: 31-32.) that describes the presence of another type of needle-like defense in the aroid family Monsteroideae (except Anadendrum and Heteropsis) and in the genera Pothos and Pothoidium. Peter describes these other ( ? ) needle-like structures (named 'trichosclereids') that were 'produced' (and clearly visible in a photo) from a dried herb. specimen of Scindapsus latifolius. Ted Held has been corresponding with me on this subject, and he has been searching for these two types of structures using one of those new-fangled SEM microscopes and photographing his findings, these micro-photos of some of the structures he has observed are truly amazing, and I am going to suggest that he send a couple to Les Kallus to be posted where they may be seen by anyone who has an interest in this aspect of our hobby. It is a little-known facet, and one of great importance to us all as these plants we so love can be BAD 'friends' at times, and to my amazement relatively little is known or published on the 'why' of their dangerous effects on humans! LOTS more research is urgently needed to find out what these plants are capable of!!! Ted has just sent me a wonderful photo of some structures , this most recent photo is of a cross-section of the crown of a Cryptocoryne usteriana, it shows piles of needle-like structures lying in bundles. Ted has 'tested' the juice of this plant by tasting it ( ! ), but no bad effects were noted. I urge Ted to forward the photos of both his findings with Dieffendachia and with Cryptocoryne to Les to be posted (if Les is agreeable) and perhaps we can get a discussion going that may add to our knowledge of these plants we so love. I will try to post Ted's recent letter to me sans the photos after this as the list does not permit attachments.. Good growing! Julius

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