The Bryophytes, comprising the two groups of Liverworts (Hepaticae) and Mosses (Musci), present a great diversity of structure, some being so delicate that good preparations are very uncertain, while others are so hard that it is difficult to get satisfactory sections. Between these extremes, however, there are many forms which readily yield beautiful and instructive preparations.
If but one fixing agent should be suggested for the entire group, it would be chromo-acetic acid with 1 g. chromic acid and 2 c.c. acetic acid to 100 c.c. of water. It should be allowed to act for at least 24 hours. For morphological study, Dr. Land uses a formalin alcohol solution (6 c.c. commercial formalin to 100 c.c. of 50 per cent alcohol), which he has tested in extensive collections in various tropical regions, where it has been impracticable to use the chromic series, with its tedious washing and changing of alcohols. Material may be left in the formalin alcohol solution until needed for use, a convenience which will hardly be appreciated by those who are always within reach of a laboratory.
For general study, the small, delicate forms may be mounted whole in Venetian turpentine.
Some of the liverworts are floating aquatics, but most of them grow on logs or rocks or upon damp ground. They are found at their best in damp, shady places. Many of them may be kept indefinitely in the greenhouse. Riccia, Marchantia, Conocephalus, Asterella, and many others vegetate luxuriously, and often fruit if kept on moist soil in a shady part of the greenhouse, and they do fairly well in the ordinary laboratory if covered with glass and protected from too intense light. Riccia natans is a valuable type for illustrative purposes. It floats freely on the surfaces of ponds and ditches. Early in the spring (during April in the Chicago region) it produces antheridia; then, for a short time (about the first of May) both antheridia and archegonia, and still later only archegonia. Sporophytes then appear as black dots along the grooves. After the spores are shed, the thallus remains sterile for the rest of the season. Marchantia and similar forms are not difficult to establish out of doors. A rather damp, shady spot close to the north side of a building is best. Scrapings from a board which has been nearly burned up make the best fertilizer to scatter on the soil, if one is to cultivate Marchantia. Such freezing as Marchantia receives in the vicinity of Chicago does not prevent it from appearing again the next spring. If it is desirable to have material throughout the year, the out-of-door culture may be made in a box which can be brought into the laboratory or greenhouse in the winter. A box 3 feet long, 2 feet wide, and 1 foot deep will be convenient. It should have a glass cover; an old window will do. There should be about 6 inches of dirt in the box. A mixture of sand, loam, and charred scrapings will make a good substratum for Marchantia. If one is to raise liverworts in the laboratory, it is absolutely necessary to note carefully the conditions under which they grow in the field.
The living plants are very desirable, since they not only furnish the best possible material for habit work and the coarser microscopic study, but they also enable one to secure complete series in the development of the various organs.
If even a small room in a greenhouse is available, liverworts can be grown in great variety and abundance. On one side of the room, have a pile of rocks. Half of this space should be occupied by limestone rocks, held in place with as little mortar as possible. There should be some shale and some porous red brick. The whole should be arranged so that water may trickle down from above. A pipe with holes 1/16 inch in diameter will furnish enough water. The other three sides may be built up of various rocks, and some clay, so as to form a table about 1 m. high. A small fountain, with a bowl a couple of feet in diameter, built of rocks, will add to the efficiency. If a few well-supported cement tanks be placed above the principal pile of rocks, Isoetes and all the water ferns may be grown there, besides Elodea, Myriophyllum, Chara, and other forms constantly needed in laboratory work.
Return to Methods in Plant Histology