Elementary botany (1898) Elementary botany elementarybotany00atki Year: 1898 FEAXS. 179 formation of a cross wall, and as it increases in length other cross walls are formed. But very early in its growth we see that a slender outgrowth takes place from the cell nearest the old spore wall. This slender thread is colorless, and is not divided into cells. Jt is the first rhizoid, and serves both as an organ of attachment for the thread, and for taking up nutriment. 370. Prothallium.—Aery soon, if the sowing has not been so crowded as to prevent the young plants from obtaining nutriment sufficien
Elementary botany (1898) Elementary botany elementarybotany00atki Year: 1898 FEAXS. 179 formation of a cross wall, and as it increases in length other cross walls are formed. But very early in its growth we see that a slender outgrowth takes place from the cell nearest the old spore wall. This slender thread is colorless, and is not divided into cells. Jt is the first rhizoid, and serves both as an organ of attachment for the thread, and for taking up nutriment. 370. Prothallium.—Aery soon, if the sowing has not been so crowded as to prevent the young plants from obtaining nutriment sufficient, we will see that the end of this protonema is broadening, as shown in fig. 220. This is done by the formation of the cell walls in different directions. It now continues to grow in this way, the end becoming broader and broader, and new rhizoids are formed from the under surface of the cells. The growing point remains at the mid- dle of the advancing margin, and the cells which are cut off from either side, as they become old, widen out. In this way the ' wings,' or margins of the bolus)- little, green, flattened body, are in advance of the growing point, and the object is more or less heart-shaped, as shown in fig. 214. Thus we see how the prothallium of ferns is formed. 371. Sexual organs of ferns. — If we take one of the prothal- lia of ferns which have grown from the sowings of fern spores, or one of those which may be often found growing on the soil Fig. 220. Young prothallium of a fern (nipho-
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