Remarques sur la biologie du thym Thymus vulgaris L.

Abstract

In the populations of Thymus vulgaris L. of South France malesterile plants are found, the flowers of which never produce pollen. The flowers of the other plants, which are said to he male-fertile, generally produce pollen. The two kinds of plants are easily distinguishable, at least in the wild state. The hermaphrodite flowers of the male fertile plants are proterandric. When they open, the gynoecium does not function. By sunny weather, the anthers immdiately burst. During two or three days, the flower functions only on the male side. After this period, the anthers dry out and the style reaches its full development; it becomes able to be pollinated but, at the beginning of this new phase, the fertilization is poor; meanwhile, as poor ns it is, it cannot be followed by another pollination. Therefore, since bee pollination is generally very active, the number of seeds set in each flower is frequently low, 0.2 to 0.5 as an average. Proterandry does not rule out the fertilization between two flowers of the same plant: inbreeding depression is, possibly, partly responsable for this low seed production of the male-fertile plants by leading to the formation of more or less lethal embryos. In female flowers, gynoecium receptivity is optimum as soon as the flower opens and the seed setting gives, everything being equal, twice as much seeds as in the hermaphroditic flowers or more. This would probably account for the rather high level of male sterility in the natural population but inbreeding depression, on the other hand, is strong enough to give a justification of the male sterility as a cross fertilizing mechanism. Experiments measuring the rate of natural self-fertilization are in progress and will permit to give its real value to each one of the two explanations. © 1975 Taylor & Francis Group, LLC.