They often grow mingled together, but with large patches consisting of one form alone. At first I thought that the two were nearly equal in number; but on examining every plant which grew close to the edge of a little overhanging dry cliff, about 200 yards in length, I found only 12 females; all the rest, some hundreds in number, being hermaphrodites. Again, on an extensive gently sloping bank, which was so thickly covered with this plant that, viewed from the distance of half a mile it appeared of a pink colour, I could not discover a single female. Therefore the hermaphrodites must greatly exceed in number the females, at least in the localities examined by me. A very dry station apparently favours the presence of the female form. With some of the other above-named Labiatae the nature of the soil or climate likewise seems to determine the presence of one or both forms; thus with Nepeta glechoma, Mr. Hart found in 1873 that all the plants which he examined near Kilkenny in Ireland were females; whilst all near Bath were hermaphrodites, and near Hertford both forms were present, but with a preponderance of hermaphrodites. (7/16. 'Nature' June 1873 page 162.) It would, however, be a mistake to suppose that the nature of the conditions determines the form independently of inheritance; for I sowed in the same small bed seeds of T. serpyllum, gathered at Torquay from the female alone, and these produced an abundance of both forms. There is every reason to believe, from large patches consisting of the same form, that the same individual plant, however much it may spread, always retains the same form. In two distant gardens I found masses of the lemon-thyme (T. citriodorus, a var. of T. serpyllum, which I was informed had grown there during many years, and every flower was female.
With respect to the fertility of the two forms, I marked at Torquay a large hermaphrodite and a large female plant of nearly equal sizes, and when the seeds were ripe I gathered all the heads. The two heaps were of very nearly equal bulk; but the heads from the female plant numbered 160, and their seeds weighed 8.7 grains; whilst those from the hermaphrodite plant numbered 200, and their seeds weighed only 4.9 grains; so that the seeds from the female plant were to those from the hermaphrodite as 100 to 56 in weight. If the relative weight of the seeds from an equal number of flower-heads from the two forms be compared, the ratio is as 100 for the female to 45 for the hermaphrodite form.
Thymus vulgaris.
(FIGURE 7.15. Thymus vulgaris (magnified). Left: Hermaphrodite. Right: Two females.)
The common garden thyme resembles in almost every respect T. serpyllum. The same slight differences between the stigmas of the two forms could be perceived. In the females the stamens are not generally quite so much reduced as in the same form of T. serpyllum. In some specimens sent me from Mentone by Mr. Moggridge, together with the sketches in Figure 7.15, the anthers of the female, though small, were well formed, but they contained very little pollen, and not a single sound grain could be detected. Eighteen seedlings were raised from purchased seed, sown in the same small bed; and these consisted of seven hermaphrodites and eleven females. They were left freely exposed to the visits of bees, and no doubt every female flower was fertilised; for on placing under the microscope a large number of stigmas from female plants, not one could be found to which pollen-grains of thyme did not adhere. The seeds were carefully collected from the eleven female plants, and they weighed 98.7 grains; and those from the seven hermaphrodites 36.5 grains. This gives for an equal number of plants the ratio of 100 to 58; and we here see, as in the last case, how much more fertile the females are than the hermaphrodites. These two lots of seeds were sown separately in two adjoining beds, and the seedlings from both the hermaphrodite and female parent-plants consisted of both forms.
Satureia hortensis.
Eleven seedlings were raised in separate pots in a hotbed and afterwards kept in the greenhouse.