By Dr. E. T. Bodenberg

Life Conditions Affecting Mosses In The Park.

For a general discussion of the topography of the park, its geographic location and climatic factors, the habitats of its plant life and the life zones on the mountain, the reader is referred to "Flora of Mount Rainier National Park", Mount Rainier National Park "Nature Notes" Vol. XVI, Nos. 1 & 2, March - June - 1938. It is safe to say that in general mosses are affected in the same way as the flowering plants by the various environmental factors.

Some of the most important of the factors affecting the variety of and the number of species of mosses in the park are summed up below.

(1) The great range of elevation from approximately 1600 feet in the southeastern part of the park up to the summit of the mountain, 14,408 feet. Mosses are distributed throughout this range of elevation with certain species characteristic of each zone. In fact, the author is of the opinion that mosses really afford better zonal indices than the higher plants.

(2) The deep forests which cover the lower elevations of the park and extend up to about 4000 feet at which point the trees become smaller and less down material covers the forest floor. The shade of the forests with the many rotting logs and soil with a high humus content provide a favorable environment for the many pleurocarpous forms which live there.

(3) Small lakes and ponds and swampy areas provide favorable habitats for Sphagnums; many small streams for water mosses (Fontinalaceae) or other aquatic forms; moist walls for the many canyons for forms such as the Bartramiaceae.

(4) Low timberline with vast areas of exposed rock which are covered by forms such as the Andreaeas and the Grimmias.

(5) The refrigerating effect of the glacial ice which covers more than 45 square miles of the mountain.

(6) Cold air drainage down the deep canyons below the glaciers which serves to help carry high altitude forms lower down.

(7) The effect of avalanches which also carry high altitude forms down the mountain sides.

(8) The blanketing effect of the early snows which often fall so rapidly as to prevent the freezing of the ground.

(9) The radiation effects brought about by the isolation of the peak which allows for rapid cooling.

(10) Old burns which have opened up certain areas for occupation by other mosses. An example of this would be a form like Funaria hygrometrica, the Twisted Cord Moss, which is found abundantly in areas where charred wood abounds. In the southeast corner of the park lowland species are afforded an opportunity of spreading up into the park.

While mosses are small plants and the average person knows little about them, yet they often form a conspicuous element of the plant life of a region because of their rapid and prolonged growth, and because of their ability to occupy and thrive in areas where other plants cannot.

In nature, one's eye is attracted by the green tufts and branching growths, although the red, brown or yellow of seta and capsule may aid by contrast of color.

Probably few other names have so often been improperly applied as "moss". While some of these plants so misnamed, as are the Liverworts, resemble the mosses, yet the majority have no structural resemblances. It must be remembered that mosses possess true stems and leaves.

Among lichens we find plants called reindeer moss (Cladonia rangiferina), match-head moss (Cladonia cristatella) and beard moss, or tree moss (Usnea barbata). All of these lichens, while they may bear some superficial resemblance to mosses, consist of an alga and a fungus living together symbiotically.

Sea mosses, like the lichens, belong in a lower group of plants - the Algae. True mosses never grow in water. The so-called Irish moss which is collected for food along the Atlantic coast, is an Algae.

The Spanish moss (Tillandsia) of the south is a flowering plant and bears flowers and seeds as does the "Flowering Moss" (Pyxidanthera), a prostrate plant of the New Jersey pine barrens.

The "Club Mosses" (Lycopodiales) belong to the Pteridophyte phylum and are more highly developed. Some Lycopodiums are known locally as "Stag-Horn Mosses".

Ecological Importance Of Mosses

Mosses are among our most important plants ecologically as they possess characteristics which enable them to act as pioneers in areas previously unoccupied by plant life. In regions such as on Mt. Rainier we can see how they push in and occupy talus slopes and bare rock cliffs. Upon drying, mosses are not quickly injured as they possess the ability to revive rapidly when moist. Their leaves are not provided with a cutinous waterproof layer as are those of higher plants, and can therefore dry quickly and absorb water through leaves and stems. While they occupy practically all habitats except salt water, they prefer cool, moist woods and swamp lands. They are particularly abundant in the temperate zones of the earth where they form typical formations. On Mt. Rainier they range in habitat from the dense shade and high humidity with mild temperatures of the Canadian Zone forests to the arid cold of the mountain top where air temperatures are never above freezing. Then there are the Sphagnums in such swampy areas as about Longmire Springs, Berkeley Park, Mowich Lake, Snow Lake and others; the Fontinalaceae grow abundantly in running water of the cold streams; Bartramias, Hygrohypnums and others grow where water seeps out from the sides of the ravines and canyons; Dicranaceae and Brachythecieae are abundant in the shelter of heather in the alpine meadows and, above on the bleak rock slopes and among pumice, are forms like Grimmias and Andreaeas.

Economic Importance Of Mosses

In this connection the Sphagnums or Peat Mosses are about the only group of importance, for in many regions of the world as in Ireland, Scotland and Northern Europe, peat is important as a fuel supply. Growing abundantly in the shallow depressions left by the glaciers as they receded from northern United States, it is estimated that our peat supply would be sufficient to last the country a hundred years in the event of necessity. Peat is also used as litter in poultry houses, as a packing material by florists in shipping bulbs and cuttings, and as an aid in growing grass on lawns and golf courses. During the World War extensive use was made of sphagnum in preparing packing for wounds. It was once estimated by the geologist Dana that 15,000,000,000 cubic feet of sphagnum are found in Massachusetts alone.

Linnaeus has related (Braithwaite, British Moss Flora, Vol. 1, Page 37), that the Laplanders use Polytrichum commune for beds, and has commended it for not harboring fleas or any infectious diseases. In northern England it is made into small dusting brooms and mats.

Ancestry Of Mosses

The ancestry of mosses is a very ancient one. Wholly or partly aquatic, these plants are often regarded as composing the first land flora.

Moss fossils yielded by geological strata are practically always identical with present-day mosses. Due to the fact that mosses lack any hard structures such as wood or lime, they had little opportunity to become fossilized. Therefore, it is very difficult to establish, by means of fossils, the time of origin of mosses. Herzog, in his Geographie der Moose, mentions that an Andreaea has been reported from the Permian and a Sphagnum from the Tertiary brown coal. But since those brown coal formations were built up in damp lowlands with a tropical climate, we cannot understand, with our knowledge of the present life conditions of the peat mosses in the temperate regions, how they could contain Sphagnum.

The Place Of Mosses In The Plant Kingdom

Mosses, together with the Liverworts, make up the second phylum, or Bryophyta, of the most commonly employed system of classification of the plant kingdom. The group is large and diversified, representing an intermediate stage in development between the very simplest organized plants, such as algae and fungi, and the higher vascular plants.

Most systems of classifications of plants are based on the progress of development of sexuality among its members. Among the Bryophytes we find that sexuality has already proceeded to a high degree and, in addition, a form of life cycle has appeared or, as it is commonly known to students of plant science, an "alternation of generations". In this life cycle, a haploid individual, known as the gametophyte, alternates with a diploid individual known as a sporophyte. The haploid individual has in its cells one-half the number of chromosomes characteristic of the body cells of the sporophyte. The life cycle of a typical moss such as Polytrichum will be considered in the section on the Life History of Mosses.

The Life History Of The Mosses

The life history of mosses is an alternation of two differently-appearing plants known, respectively, as gametophyte and sporophyte. The former generation, which is greenish in color and asexual, is the common, leafy moss plant familiar to most persons. The stages in development of the successive generations will be taken up step by step, starting with the spore which is produced in the capsule of the sporophyte plant. The stages of the two generations are given below:

PLATE I. Showing the Alternation of Generations of the common Hair-Cap Moss, Polytrichum.

Figs. 1 to 8a, inclusive represent gametophyte generation; Figs. 9 to 13 are the sporophyte generation. Fig. 1 - tetrad; Fig. 2 - spore; Fig. 3 - protonema; Fig. 4 - protonema with bud; Fig. 5 - leafy shoot; Fig. 6a - archegonial plant; Fig. 6b - antheridial plant; Fig. 7a - archegonium; Fig. 7b - antheridium; Fig. 8a - egg; Fig. 8b - antherid; Fig. 9 - zygote; Fig. 10 - leafy plant with young sporophyte; Fig. 11 - mature sporophyte; Fig. 12 - capsule showing teeth; Fig. 13 - spore mother cell (The cycle then repeats again).

The gametophyte generation of a moss begins with a small cell in the capsule, known as a tetrad, or tetraspore. (Fig. 1). They are so-called because they are produced in groups of four from a spore mother-cell, the last stage of the sporophyte generation.

When the four spores break apart upon maturity, each is a small, one-celled haploid cell known as the asexual spore. (Fig. 2). If these spores are mounted in water for microscopic examination, they appear greenish because of included chlorophyl. Whenever the spores fall to the ground upon being freed from the capsule, they germinate and produce tiny, green threads known as protonema. (Fig. 3). These protonema grow rapidly and soon branch profusely, forming a felted growth which covers the substratum, or medium in which the moss grows. Little lateral swellings soon appear, and these develop into buds. (Fig. 4) These buds increase in size and become the leafy shoots (Fig. 5) which soon take on the appearance of the familiar moss plant as stems and leaves differentiate. At the base, small out growths, known as rhizoids, grow out; unlike the roots of higher plants, these serve merely as absorbing organs. Moss plants may be distinguished from liverworts from the fact that they usually have their leaves spirally arranged and not in one plane as do the liverworts. The protonema now usually disappear completely, although sometimes they persist and do the photosynthetic work of the leaves.

The reproductive organs develop in the midst of a cluster of leaves either at the tip of the stems of plants, or of small lateral branches. Each group with its involcucral leaves constitutes a receptacle. These receptacles have been improperly referred to as "moss flowers", and the male receptacles of Polytrichum do have a flower-like appearance (Fig. 6b), but they are in no sense structurally similar to the flowers of higher plants. The female receptacle is shown in Fig. 6a of the life cycle. Moss plants are said to be homothallic when they bear antheridia (Fig. 7b) and archegonia (Fig. 7a) on the one plant, and heterothallic when the sex organs are borne on separate plants.

Thousands of male sex cells, known as antheridia or sperms, are found in the long and narrow sac-like antheridia which are composed of a single layer of cells except where they are attached to the stem of the plant. When the antheridium is mature, the end of the structure away from the stalk bursts and the sperms are released in a mass. Each sperm (Fig. 8b) consists of a long, curved nucleus surrounded by cytoplasm and bearing two long, whip-like flagella at one end.

The archegonia (Fig. 7a) are flask-shaped structures composed of an upper, narrow portion - the neck - and a swollen, lower portion - the ventor. The egg (Fig. 8a) is borne in a ventor. At first the neck is composed of a solid mass of cells, then the center row disintegrates and a narrow passage - the neck canal - results, connecting the ventor with the exterior.

During periods of moisture, with dew or rain, the motile sperms swim to the archegonium and down the neck where the egg cell is fertilized. The resulting cell is the zygote, or oospore (Fig. 9), and since ito contains the diploid number of chromosomes, is the beginning of the sporophyte generation. The zygote lives almost entirely by absorbing food material from the leafy plant. At its base it develops an absorbing organ - the foot.

The first evidence to the unaided eye of these sporophytes (Fig. 10), is the appearance in Polytrichum of the small "lances" which may appear at almost any season of the year. The sporophyte grows rapidly, and a stalk and sporangium appear. Often chlorophyll develops, and photosynthesis is carried on. As the stalk elongates during the early growth of the sporophyte, it sometimes breaks the archegonium loose and carries it to the top of the sporangium to become the hood, or calyptra. (Fig. 11). This hood drops off at maturity and the capsule opens by a circular lid - the operculum - which easily detaches itself from the lower portion of the capsule when the spores are ripe. In this way the release of spores is allowed, a release which is regulated by a fringe of five teeth - the peristome - around the edge of the capsule, and in the case of Polytrichum, by small openings in the membrane beneath the operculum (Fig. 12), making the capsule a sort of "pepper-box" for scattering the spores.

Capsules are differentiated into three areas: (1) A capsule wall composed of layers of chlorenchyma and parenchyma; (2) A sporogenous or spore-producing area; and (3) A central columella. In the sporogenous area each cell, or spore-mother cell (Fig. 13), by sporogenesis forms a tetrad (Fig. 1) of haploid cells or tetraspores. These cells are tetrahedral in shape and are composed of cytoplasm, nucleus, and a single chloroplastid and some reserve food usually in the form of fat. As these break apart upon release from the capsule, they form the familiar asexual spores. Thus the life cycle is completed.

Introduction continued...