Matériel et méthodes

Principes de la procédure d'échantillonnage

Le 1^er point à clarifier est la zone exacte où l'événement inconnu (EI) a atterri ou a été au contact le plus proche avec l'environnement. Dans le cas présent, ceci fut l'objet d'un rapport de police désigné comme le P.V. n° 28, 9-1-8 1, lié à une trace circulaire visible sur le sol.

Puis, un axe écologique devrait être choisi, le long duquel une série de plantes ou d'animaux sédentaires appartenant aux mêmes espèces peut être trouvé par intervalles. Cet axe devrait traverser la "zone de contact" de l'EI et de préférence rejoindre l'épicentre.

La zone d'atterrissage, visible au sol ground, faisait environ 2,5 à 3 m de diamètre et des plantes of a wild strain de luzerne, Medicago minima, furent trouvées à l'intérieur, sur la trace, et tout du long de la zone environnante. Cette espèce fut ainsi choisie comme le modèle biologique.

Les 1ers échantillons furent recueillis par la police locale en bordure de la trace (point A) et en un point situé à 20 m (point B) comme échantillons de contrôle dans les 4 jours après l'observation de l'EI.

Le 2^ème lot d'échantillons (points C à G) fut recueilli dans les 40 jours après le jour d'observation par une équipe de techniciens du Centre National d'Etudes Spatiales. Il devrait être noté que personne d'autre que l'auteur ne savait à l'avance quand, où et ce qui devait être recueilli. Ceci atténue le risque que des artefacts puissent être produits par des auteurs de canular.

Un dernier lot d'échantillons (points H à L) fut ensuite recueilli le long du même axe, mais 2 ans plus tard (i.e.,en février 1983) the same plant species were growing on the site, but, of course, samples could not be collected at exactly the same distances. Table 1 indicates the position of the various samples along the axis.

Living plants were taken with a large clod of earth and immediately driven to the laboratory and frozen, except sample (A, B), which was transported by policemen in paper sacks.

In sample (A, B), the plants looked rather dry, but without any sign of burning. In all other samples, the alfalfa leaves, of various size, were quite similar in aspect. No visible morphological alteration was discernible after examination under a Meopta DM23 binocular microscope.

Procédure biochimique

Samples of 100 mg (fresh weight or equivalent) of young leaves (2 to 3 mm with 7.0 ± 3.6 mg average weight by leaf) were ground in Potter homogenizers with chloroform. Older leaves, which were present in samples A and B, were also analyzed. After 5 mn centrifugation at 5,000 g, the lipid phase was recuperated and concentrated under low pressure to a final volume of 5 µl per mg. These extracts were spotted on thin layer plates, and the various pigments (chlorophylls and derivatives, carotenoïds, quinons, and chromenols) separated according to the previously described techniques. Chromatograms were recorded at 425 nm using a CS920 densitometer.

The pellets were resuspended and homogenized in a mixture of water-ethanol-pyridine-acetic acid (80-10-5-5 v/v) for extraction of carbohydrates and free amino acids. Volumes were adjusted to 0. 5 µl per mg. Quantitative thin layer chromatographies were performed as previously described for carbohydrates (Bounias, 1976, 1980a) and amino acids (Bounias, 1980b).

The pH of the soil was determined after homogenization of 5 g of the earth clod in 100 ml water.

Méthodes statistiques

Means and SD calculated from (N) determinations were used in student's t test for comparisons. Variances were compared using Fisher's F test. The probabilities of significances corresponding to these comparisons and to the correlation and regression (least square method) calculations, were determined from the equations of distribution of t and F. For correlation coefficients (p), the "t" value was calculated from: t = [gamma· p²/(1 - p²)]^1/2 where v = degree of freedom = N - 2. The standard deviations of the regression slopes (b) was calculated from: sigma_b = [(b/p)² - b²)/v]^1/2. The slopes corresponding to two aleatory variables plotted together are given byd= b/p.

Additionally, in (D+ 370) control samples ("H" to "L"), considered as likely representative of the natural biological variability on the site, correlations with distances to the epicenter were artificially increased by switching the values of the two parameters situated at the extreme parts (i.e., H and L) to their upper and lower possible values, (or reversally), taking into account the range of their standard deviation. Then, correlation calculations will give an estimation of what can be considered as the strongest "fortuitous" correlation, in conditions where no particular correlation is expected. The following notations will be used in the text for the regression slopes: b_E for exposed to the event (A to G); b₀ for controls (H to L); b_r for reconstituted theoretical extreme values in controls.

Only the major features will be represented here.