. Botany for high schools. Botany. 212 GENERAL MORPHOLOGY OF PLANTS pendently of other plants. They obtain their mineral and nitrog- enous foods from the water, while they fix the carbon from the carbonic acid absorbed from the water, in the presence of the chlorophyll and sunlight. The characters of structure and reproduction should be studied in connection with the individual plants. 349. GREEN ALG^* (CHLOROPHYCE^). The Conjugating Green AlgcB (Conjugatce), Spirogyra.—The plant spirogyra lives in fresh water in ponds, the borders of lakes, or in pools. Sometimes it is found in very slow-runn
. Botany for high schools. Botany. 212 GENERAL MORPHOLOGY OF PLANTS pendently of other plants. They obtain their mineral and nitrog- enous foods from the water, while they fix the carbon from the carbonic acid absorbed from the water, in the presence of the chlorophyll and sunlight. The characters of structure and reproduction should be studied in connection with the individual plants. 349. GREEN ALG^* (CHLOROPHYCE^). The Conjugating Green AlgcB (Conjugatce), Spirogyra.—The plant spirogyra lives in fresh water in ponds, the borders of lakes, or in pools. Sometimes it is found in very slow-running water. It is in the form of simple threads or filaments which may be quite long and are unbranched. Large numbers of these threads are tangled together into a mat which floats in the water. Much gas which is given off during photosynthesis is caught in the meshes of the tangle, buoys the mat of the alga up to the surface of the water where the light is more efficient, and gives the plant a frothy appearance, which sug- gested such names as pond scum," frog spittle," etc. The threads are made up of cells w^hich are cylindrical in form and * To THE Teacher. The number of green algae studied must be determined by the teacher,. 170. Fig. 169. Fig. Spirogyra Spirogyra before plac- in 5 per cent ing^in salt salt solution, and will depend to some extent on the time, the facilities, and material at hand. If only one is studied carefully it preferably should be Spirogyra. If two, then Vaucheria or (Edogonium should be included because of the differentiation of the sex organs. In more advanced classes the shield Coleochaete might be included. In addition to laboratory work, such portion of the text should be studied as the teacher finds time and adaptability of the pupils will permit. The general features of the plant body, the progression from single cells to threads and cell plates, the general features of sex organs and their differentiation into two kinds, as well as
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