Partitioning and diversity of nuclear and organelle markers in native and introduced populations of Epipactis helleborine (Orchidaceae).

Variability of allozymes (1170 individuals, 47 populations) and chloroplast DNA (692 individuals, 29 populations) was examined in native European and introduced North American populations of Epipactis helleborine (Orchidaceae). At the species level, the percentage of allozyme loci that were polymorphic (P(99)) was 67%, with a mean of 2.11 alleles (A) per locus, and an expected heterozygosity (H(exp)) of 0.294. At the population level, mean P(99) = 56%, mean A = 1.81, and mean H(exp) = 0.231. Although field observations suggest that self-pollination occurs frequently, populations had a genetic structure consistent with Hardy-Weinberg expectations and random mating (mean F(IS) = 0.002). There was significant deviation from panmixia associated with population differentiation (mean F(ST) = 0.206). The distribution of two chloroplast haplotypes showed that 15 of the 29 populations were polymorphic. Using both nuclear and organelle F(ST) estimates, a pollen to seed flow ratio of 1.43 : 1 was calculated. This is very low compared with published estimates for other plant groups, consistent with the high dispersability of orchid seeds. Finally, there was no evidence for a genetic bottleneck associated with the introduction of E. helleborine to North America.

Low potassium and high calcium thresholds for spontaneous ventricular fibrillation in Langendorff-perfused rabbit hearts.

Consistent threshold concentrations were determined for the precipitation of spontaneous ventricular fibrillation in isolated rabbit hearts by reduction of potassium or increase of calcium in the perfusion solution. The low potassium threshold was a function of the calcium concentration: it increased from 0.81 +/- 0.14 mM (mean +/- SD) with 1.0 mM calcium to 1.58 +/- 0.17 mM with 5.0 mM calcium. The high calcium threshold was 12.8 +/- 2.1 mM at 5.6 mM potassium. Consistent thresholds could not be established when the calcium concentration was greater than 5 mM and potassium concentration less than 3.6 mM. The absolute low potassium and high calcium thresholds did not depend on the potassium and calcium concentrations of the control perfusion solution, being the same whether these were "conventional" (5.6 and 2.25 mM, respectively) or "physiological" (3.6 and 1.6 mM). Spontaneous fibrillation appeared sooner when precipitated by high calcium than when precipitated by low potassium. Many other arrhythmias were observed; these were neither sufficient nor even necessary precursors of spontaneous fibrillation. Particularly with high calcium, spontaneous fibrillation could be the first arrhythmia to appear. Hearts perfused with hypertonic McEwen's solution were more susceptible to the precipitation of fibrillation by low potassium than those perfused with more physiologically balanced solutions. Enhanced susceptibility to precipitation of fibrillation by high calcium concentration was not seen.

Ventricular fibrillation thresholds in Langendorff perfused rabbit hearts: all or none effect of low potassium concentration.

The median single pulse ventricular fibrillation threshold of 56 determinations in eight isolated rabbit hearts perfused with a Krebs-Henseleit solution was 36 mA, with a range from 12.5 to above 50 mA. The fibrillation threshold remained in the same range when the potassium concentration in the perfusing fluid was decreased from its normal 5.6 mmol.litre-1 to as low as 1.8 mmol.litre-1. A further decrease in potassium concentration reduced the fibrillation threshold to a median value of 1.6 mA in nine determinations on six hearts. With a 1.6 mmol.litre-1 potassium concentration, thresholds were in either the high or the low range depending on the individual heart. A pronounced shortening of refractory period and an earlier vulnerable period were associated with the sharp change in fibrillation threshold; the diastolic extrasystolic threshold, cycle length, and RT interval duration increased in a more linear manner as the potassium concentration was lowered.

Calcium precipitation from mammalian physiological salines (Ringer solutions) and the preparation of high [Ca] media.

The maximum nonprecipitating concentration of calcium in a bicarbonate-buffered Krebs-Henseleit-type mammalian physiologic saline at 25 degrees C has been established as 10 mM in the presence of 1 mM phosphate, and as 18 mM when phosphate is absent. At 38 degrees C, the respective limits are 5.6 mM with the phosphate, and 16 mM in its absence. At its physiological concentration of 1.6 mM, calcium precipitation also appeared in solutions of pH greater than 9. When phosphate was present, the precipitate appeared immediately, but redissolved once pH was reduced below 7.8; in the absence of phosphate, precipitation of calcium carbonate became visible only after 3-4 min, but this precipitate would not redissolve even at pH 7.4. As carbonated stock bicarbonate solution gradually loses CO2 and becomes alkaline, a protocol for mixing physiologic salines using alkaline bicarbonate stock was developed. Calcium precipitation can be avoided if, before calcium is added, the bicarbonate-containing bulk solution is gassed with 5% CO2 for 15 min at a flow of 0.5 liter/min per liter of final solution.

A generalized mechanics of articular swings. II. From kinematics to cadavera.

The kinematics of swings at joints can be described fully by means of two simple ratios and the angle at which the total operative force vector pulls upon a bone. The ratios can be applied to individual muscles, thus linking structural and functional myology in an exact way. The 'spurt' and 'shunt' types of muscle are sharply distinguished, both kinematically and anatomically.

The logical aspects of evolution.

CONCLUSION: It would seem then, that the concept of evolution can be arrived at by a deduction from an axiom applicable to the descendants of a pair of bisexually reproducing ancestors, but excluding hermaphrodites. The generalization of the concept to cover all other organisms, including hermaphrodites, must be by an induction from the results of the said deduction. Such is the logic of the affair.