It will be recalled that in 1994 Comet Shoemaker-Levy crashed into Jupiter. When Lawrence Edwards was investigating the profile shapes of leaf buds (i.e. their lambda values) he found that they vary rhythmically with a two-week cycle, except when in the neighbourhood of electric and/or magnetic fields. The original observation concerned a tree near a transformer, so to test the idea (and avoid waiting for trees to grow near transformers!) he checked the behaviour of knapweed (centaurea scabiosa & nigra) which could be checked under electric cables. The suppression of the two-weekly rhythm was indeed verified for such plants, but not if they were remote from cables. The two-week rhythm correlates with the conjunctions and oppositions of the Moon and a planet depending upon the tree. This is the first scientific evidence of a traditionally held relationship between trees and planets, now well verified by thousands of observations (predictably scoffed at by the New Scientist reviewer of Reference 7). In the case of knapweed the planet is Jupiter. By 1994 Edwards had made many observations of knapweed and so could compare its behaviour that year against the norm, and the result was interesting indeed, as illustrated below.
The upper and lower dotted lines show boundaries outside which no lambda values had ever been observed for this plant, before or since. The 1994 line shows values well outside these limits, suggesting that the comet impact affected the forms of the plant buds.