Of the Seeds of Mosses.
The seeds of mosses vary very much in surface, in size, in figure, and in colour. In surface, the greater part of them are quite smooth and round, yet some are angular—the seeds, for instance, of Phascum sei ratum ; sonic are mai kecl with circular depressions, as in Enca lypta vulgaris; some are echinated, as in ninostornum pyriforme, Bartramia ponniformis, &c. In size, it is re markable, that, as in cotyledoneous plants, sonie of the minute species have much larger seeds than species of larger growth. Thus, in Pnascuin serratum, the mi nutest of mosses, the capsules of which contain 100 seeds, the seeds are larger in proportion than those of all the other Phasca, with the single exception of Phascum alternifoliurn, which contains sixteen very large seeds in each capsule. Similar variations in size occur in other genera. In figure, the seeds of most mosses are spheri cal, or approach to that forni ; yet in Phascum serratum an instance has been given of angular seeds, and in a con siderable nunibcr of species, they are more or less oval. In colour, at first shades of yellow and green prevail in the seeds of mosses, afterwards of brown, but in both states the colour is subject to diversities.
The seeds of mosses are so minute, that their struc ture can be well investigated only in the process of germination.
Meese, in 1767, was the first to raise mosses from the seed. His experiments were made upon Polyttichum commune ; but far more satisfactory experiments, and, indeed, experiments altogether conclusive, are those of Iledwig himself.
He seems to have been led to these experiments from an occurrence in May 1774. To a strong north wind for a night and day, succeeded cloudy, wet, and cold weather. In a few days afterwards, the earth in the flower-pots in his windows looking to the east, assuined a greenish hue. He conjectured this to be owing to young plants of mosses. Taking up some of them on the point of a penknife, cleansing them in a few drops of water from the adhering earth, and subjecting them to his microscope, he observed a young plant, with pellucid, very white roots, and above them some minute tin earls, delicately articulated in some parts. These threads lie
conjectured to be cotyledons, and immediately began to think of experiments for ascertaining- farther this point. 'rhe species which lie selected for this purpose was Fu naria hygrometrica. Remembering that Dillenius states it to love arid and adust places, he made a soil for it, in a flower-pot, above common earth, of about an inch thick of ashes and charcoal intermingled, adding a very little earth to the composition. Over this he opened, with the point of a needle, several capsules of Funaria hygrome trica, the seeds being dispersed in little heaps. The seeds of other capsules, opened in the same manner, he scattered more equally over the flower.pot. That the seeds might not be blown away by the winds, he covered the flower-pot with well-washed branches of boxwood, and placed the flower-pot in one of his windows with a northern exposure.
In the first days after the sowing the yellowish heaps contracted a darker colour. Afterwards they could scarcely be seen by the unassisted eye. But on the seventh day from sowing, with the help of a moderately magnifying glass, he found the whole surface of the pot, and particularly the little heaps, of a greenish colour. The branches of boxwood were now taken away, and, having taken up some plants on the point of a needle, washed them, and placed them under his microscope in a drop of water, lie saw with much pleasure, swim ming in it, innumerable seeds, part of which had already produced a simple, very tender, pellucid, white root, and immediately opposite a simple obtuse corpuscle, of a very light green.
Three days afterwards, or on the tenth day, the whole surface of the llower-pot was covered with an agreeable green colour, and the little heaps had acquired a silky lustre. He now found the radicles increased either in number or by ramification ; and the cotyledons branched. Eight days afterwards, there was no change, except that the whole was of a more intense green, and afterwards he perceived the leaves springing here and there.