Green algae: observation



For experiments in most phases of botanical microtechnic, no group of plants affords better material than the green algae, since the killing, fixing, and staining, can be watched directly. Learn fixing, and staining can be watched directly; the effect of the change from one solution to another can be observed; and even the behavior during infiltration with paraffin can be determined with considerable accuracy.

Since the Chlorophyceae furnish our best illustrations of the evolution of the plant body, the origin and development of sex, and also the beginning of alternation of generations, they occupy a prominent place in any well-planned course in the morphology of plants; and, if they were better known, the ease with which the reactions of the individual cell may be observed would make them valuable to the physiologist.

They are found in both fresh and salt water, but are most abundant in fresh water. The ponds, ditches, and rivers of any locality will yield an abundance and variety both of the unicellular and the multicellular members of this group. Most of the forms are independent, but there are epiphytic, endophytic, and saprophytic species. The larger forms and those which grow in tufts or mats are readily recognized in the field. Many of the smaller forms are attached to other water plants. Drain the water plants and then squeeze them over a bottle. The sediment is likely to contain a variety of unicellular and other small algae.

Many of the genera are easily kept in the laboratory. It is not necessary to have very large aquaria. Ordinary glass battery jars holding about a gallon are good for most forms. Jars holding 2 gallons will be as good or better. For some cultures which are to be kept for a long time, like Scenedesmus, small glass jars, or dishes, with ground-glass tops are desirable. For a limited amount of material, quart or 2-quart fruit cans are very efficient. Put about an inch of pond dirt in some, clean sand in others, and in still others use a gravel bottom. Many forms grow well without any soil or sand in the bottom of the jar.

When possible, use the water in which the algae were growing, since very few take kindly to a sudden change of water. If the material has been brought to the laboratory in a very small quantity of water, fill the jar about two-thirds full with tap water. Let the water run for 2 or 3 minutes before you fill the jar, since the water standing in the pipes is injurious, or even fatal, to most algae. Add water occasionally, only a little at a time, to compensate for evaporation. If the water has evaporated until the jar is about one-third full and you fill it nearly to the top with tap water, you are likely to kill some of the most desirable forms.

It is a mistake to put too much material into ajar. A wad of Spirogyra half as large as one's finger is as much as should be put into a gallon jar. As it grows to ten or twenty times that amount, it is not necessary to keep throwing it out, since it will gradually accommodate itself to conditions. However, do not let the jar become choked with the material.

Cultures may be started even in the winter. Bring in some mud over which algae were growing the previous summer or autumn; put it into a jar and fill it two-thirds full of tap water. Also bring in sticks, leaves, and stones from good alga localities and put them into jars of tap water. Cultures may be started either by taking mud "and sticks from under the ice or by taking them from places which have entirely dried up during the summer or autumn. A few such jars will be likely to yield a variety of material.

If you have a good jar of Oedogonium, or some other desirable form, do not throw it out if the alga should disappear. Remember that temporary disappearances occur in nature. Allow the culture to become dry and then set it aside where it will be protected from dust. After a few months, pour on tap water and it .is very likely that you will soon have a good jar of Oedogonium. Many algae behave similarly; some, like Volvox, appear for a short time and then disappear for a long time; some, like Cladophora, may last the whole year and grow so luxuriantly that the excess material must be removed; and some, like Ulothrix, we have not been able to cultivate at all in the laboratory.





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