The Phaeophyceae, or brown algae, are almost exclusively marine. They include a great variety of forms, ranging from delicate filaments to coarse, leathery plants 100 feet in length. There are no unicellular members.
For fixing marine algae, fixing agents should be made up with sea-water, never with fresh water, and the washing should be done with sea-water; but fresh water should be used in making the series of alcohols. When the Venetian turpentine method is to be used, wash in fresh water before placing in the 10 per cent glycerin.
For habit work, material may be put into formalin-about 6 c.c. commercial formalin to 100 c.c. of sea-water-and kept there indefinitely. If it is desired to transport large quantities of coarse forms, the material may remain in this solution for a week and may then be removed from the liquid and packed in closed pails or tubs or any water-tight containers. After reaching its destination, the material should be put into formalin again.
For material to be mounted by the Venetian turpentine method, 6 to 10 per cent formalin (always in sea-water) is a good fixing agent. Wash in sea-water for 1 hour, then in equal parts sea-water and fresh water for 1 hour, then in fresh water 1 hour. The material is now ready for staining in aqueous stains, or for the 10 per cent glycerin, if alcoholic stains are to be used.
The following formula by Flemming will also give good results, both for the Venetian turpentine method and for the paraffin method:
Chromic acid.............................1 g. Glacial acetic acid....................0.4 c.c. Sea-water..............................400 c.c.
Fix 24 to 48 hours and wash 24 hours in running sea-water. A convenient washing-box can be made from an ordinary washtub. Bore a dozen 3/8-inch holes in the bottom; insert rubber tubes 6 inches long, and in the end of each tube place the glass part of a pipette. The tub may be elevated by nailing three narrow boards to the sides so as to form a tripod. Place the bottles or cans of material under the pipettes and let sea-water flow into the tub.
If such chromic-acid material is to be used at once for Venetian turpentine mounts, follow the washing in sea-water by 1 hour's washing in equal parts sea-water and fresh water (not necessarily running water) and then 1/2 hour's washing in fresh water. The material is now ready for an aqueous stain or for 10 per cent glycerin. If desirable to keep it for future staining, put it into 5 or 6 per cent formalin in fresh water.
Material for sections may be treated in the same way, but it is often better to add 2 to 10 c.c. of 1 per cent osmic acid to 100 c.c. of the chromic-acid solution. The 1 per cent osmic acid should be made up in distilled water.
Small filamentous forms, if they are to be mounted whole, are usually more satisfactory to handle if fixed in formalin. A strong solution, about 10 c.c. of commercial formalin to 90 c.c. of sea-water, is very good. Material is well fixed in a few days, but may be left here until it is needed. To make preparations, wash in fresh water and follow the Venetian turpentine method.
For habit demonstrations many of the smaller forms can be floated out and dried on paper. Ectocarpus, Desmotrichum, Dictyota, Cutleria, and even small specimens of Laminaria are quite useful when prepared in this way. Take a light pine board, a little larger than the standard herbarium sheet, float it in a tub of water, place on the board the paper upon which the material is to be mounted, arrange the material with a toothpick or the blunt end of a needle, dipping all or a part of the board under water whenever necessary. Cover with a piece of cheese-cloth, add a blotter or two, as in case of flowering plants, and dry under gentle pressure, changing the blotters frequently. The algae have enough mucilage to make them adhere to the paper. Coarse forms, like Fucus, may need to be held down by strips of gummed paper.
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