David R. Hershey dh321 at PGSTUMAIL.PG.CC.MD.US
Thu Oct 16 00:39:27 EST 1997

I just remembered an observation that might be of interest in your
investigation of tropisms. I once grew the houseplant, common
philodendron (Philodendron scandens subspecies oxycardium) in a window and
noticed the leaves grew toward the window (positive phototropism) and the
aerial roots grew away from the window (perhaps negative phototropism) and
reached a length of over 5 cm. 

This popular houseplant is widely available and easy to grow. You might be
able to find some plants in nurseries, malls, offices, or homes and make
some observations to see if negative phototropism of roots seems a viable
hypothesis. Since it has aerial roots, cuttings are also easy to root. 
Wear gloves if you cut the stems to take cuttings because the sap contains
crystals of calcium oxalate, which cause a poison ivy-like rash due to a
mechanical injury similar to that caused by fiberglass. The rash only
occurs if you get the sap on your skin, not by just touching the plant as
with poison ivy.

David R. Hershey

Snail mail: 6700 Belcrest Road #112, Hyattsville, MD 20782-1340

Adjunct Professor, Biology/Horticulture Dept.
Prince George's Community College, Largo, MD 20772-2199

Email: dh321 at


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