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THE LIVERWORTS. — Liverworts are mosslike plants which inhabit moist localities, some living in or on the surface of water, others on rocks or damp soil, and some even growing on the bark of trees. The liverworts have an irregular thallus-shaped or platelike body. Rhizoids are developed from the lower surface of the body. From the plant body arise upright structures which bear the antheridia and archegonia.

Their life history is nearly that of a moss. These plants may also reproduce themselves asexually by means of budlike structures called gemmæ, The gemmæ, which are formed in cup-shaped organs on the upper surface of the plant, break off and under favorable conditions may form a new plant.

ECONOMIC VALUE OF MOSSES.-The mosses and their allies have little direct economic value. Indirectly they are of much benefit to mankind. In many localities they form a soft carpet, which is of great importance in holding water in the soil; thus they prevent erosion. They give off not a little oxygen to the atmosphere and must use considerable carbon dioxide in their manufacture of starch.

THALLOPHYTES

We have already defined a thallus as a plant body which has no definite root, stem, or leaf. It may be platelike, ribbonshaped, threadlike,, globular, or even irregular in form.

The thallus plants may be grouped in two great divisions: the Alga, water-loving thallophytes containing chlorophyll, and the Fungi, thallus plants which do not contain chlorophyll.

Fungi, Parasites, and Saprophytes. As a direct result of the lack of chlorophyll in the cells, the fungi are unable to make their own food. They must obtain food from other plants or animals. Some take up their abode upon living plants or animals (in which case they are called parasites); others obtain their food from some dead organic matter. The latter are called saprophytes. The above facts make the group of the fungi of immense economic importance to man. Much of the space devoted to the fungi will be given up to a consideration of the relation of parasitic and saprophytic plants to their hosts, the living or dead organisms from which they obtain their food.

Mold. One of the most common of all our fungi is the black mold (Rhizopus nigricans).

Experiments to determine the Growth of Mold. - Place a piece of bread in each of two wide-mouthed bottles or jars, add a little water, and ex

pose both jars to the air of the living room or kitchen for five minutes. Then cover both jars and plunge one into boiling water for a few minutes. Now place the jars side by side in a moderately warm room for two or three days. In which jar does growth appear first? Do both jars have like

m

Experiment with mold on bread; A, in a living room; B, in an ice-box; C, above the stove in a kitchen.

growth of mold in the given period of time?

Other experiments may be performed to show the relation of the growth of mold to light, to different degrees of moisture and to different temperatures. Why do things get moldy in a damp locality quicker than in a dry one? How would you account for the growth of mold inside of a jar of preserves or jelly? Can you determine by experiment whether black mold uses oxygen in its growth?

Directions for Growth of Mold. Bread mold may be conveniently grown for laboratory use in small shallow dishes (Syracuse watch glasses, Petri dishes, or butter chips). If bread is exposed to the air for a few minutes and then left in the covered dishes for a day or two, with a bit of wet sponge or blotting paper in the dish to keep the air moist, a good supply of mold may be obtained in a convenient dish for observational purposes.1

Observations on Mold. Examine the tangled mass of threads which cover the bread. This is called the mycelium, each thread being called a hypha. How do the hyphæ appear to be attached to the bread? Many of the hyphæ are prolonged into tiny upright threads, bearing at the top a little ball. With the low power of the microscope the structure of a sporangium may be made out. The dark-colored

ones are full of ripe spores, which may be seen by lightly tapping the cover slip over the slide. How do the spores normally get out of the sporangium? Try to find some young sporangia and note the differences in size and color between them and the older ones. Draw a series of sporangia as seen under the low power.

This method of the production of spores is evidently asexual. These spores, if grown under favorable conditions, will

r

Bread mold; r, rhizoids; s, sporangium.

produce more mycelia, which in turn bear sporangia. It has been. found, however, that at some time during the life of the mold another method of reproduction is likely to occur.

1 See Hunter and Valentine, Manual, page 83.

A

B

Formation of Zygospores.-Two hyphae which are close-lying put out threads which communicate. The end of each of the threads cuts off a cell, and the two cells, each from a different hypha, flow together and mingle. In this condition they remain as a single resting cell. This cell, which puts a heavy wall around itself, is called a zygospore. In the process we called fertilization, we found that the two cells which united to form one cell were of different sizes. Here the cells are of the same size. When two cells of the same size unite to form a single cell, we call the process conjugation. The ultimate result of the conjugation of the two cells is that a new plant grows from the zygospore after a period of rest. During the resting stage the spore may undergo very unfavorable conditions, even to extreme dryness, heat, or cold. The use of the zygospore to the plant is evidently to continue the species during an unfavorable time in the life history of the plant. The process of conjugation is possibly a sexual process. Its significance is not well understood. Is there then an alternation of generations in the mold? Physiology of the Growth of Mold. Mold, in order to grow rapidly, evidently needs considerable moisture and heat. It obtains its food from the material on which it lives. This it is able to do by means of a digestive ferment which the hyphæ pour out, somewhat as the root hairs secrete acid. The ferment is given out by the rhizoids or rootlike parts of the hypha, by means of which the mold clings to the bread. The digestive ferment changes the starch of the bread to sugar. Thus the plant is enabled to absorb the material. The food is then changed into

Conjugation of black mold; A, B. C, D, successive stages in the formation of the zygospore.

D

It seems to have been proved recently that zygospores are formed by the union of two cells, from different filaments, one of which has male, the other female characters.

HUNTER'S BIOL.-11

of the cap. These are the gills. If you place the cap of a mushroom gills downward on the surface of a piece of white paper, being careful not to disturb for at least twelve hours, it will be found that when the cap is removed a print of the shape and size of the gills remains on the paper. This is a spore print. It has been caused by the spores of the plant, which have fallen from the place where they were formed between the gills to the surface of the paper.

it in the same manner as did the hyphæ of black mold. The mushroom is a saprophyte. No sexual stage has yet been discovered.

POISONOUS MUSHROOMS. - Fungi of the mushroom species are classed by botanists as edible and inedible. The latter are popularly known as toadstools. It is difficult to give the beginner any stated rules by which to distinguish the inedible from the edible species. A few general rules may be given, however, to the collector:

Do not use mushrooms that are old or black.

Never collect those with swollen bases surrounded with saclike or scaly envelopes. (Such a structure forms the so-called death cup of the deadly Amanita.)

Do not collect mushrooms in the early stage known as buttons.
Do not use mushrooms with a milky juice.

Avoid fungi with a weblike ring around the upper part of the stipe. Be very cautious about trying new varieties. Better learn one or two edible species and stick to them. Beginners may safely eat any of the club or coral fungi found growing on dead trees in damp woods; also young puffballs and the morels, with

their characteristically ridged surface.

FOOD VALUE OF MUSHROOMS.The food value of the edible mushroom has been much overestimated. Recent experiments seem to show that, although they have a slight food value, they are far from taking the place of nitrogenous foods, as was formerly believed by scientists.

SHELF FUNGUS.-A near relation to the mushroom is the bracket or tree fungus. This fungus is familiar to any one who has been in a forest in this part of the country.

An examination of specimens shows that the shelf or bracket is in reality a spore case, which is usually provided with a very considerable number of holes, slits, or pores in which the spores are formed. The spores, when ripe, escape from the under surface of the spore-bearing body through the The mycelium is within the tissue of the tree.

minute pores.

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