FOSSIL PLANTS 



339 



those of Marsilia. Having no chlorophyll, they depend upon food 

 stored in the megaspore, as in Marsilia and Selagindla. The 

 young sporophyte also makes use of food in the megaspore as 

 in these other two heterosporous pteridophytes above mentioned. 

 The sperms (Fig. 292, B] are some- 

 what coiled and many-ciliate, re- 

 sembling in this respect those of 

 the Filicinece. The life-history 

 formula is the same as that of Sel- 

 agineUa (Sec. 326). 



FOSSIL PLANTS AND COAL 



329. Fossil plants. Plant re- 

 mains are not generally preserved 

 as fossils, partly because they do 

 not often have hard parts, such as 

 the shells and bones of animals, 

 and partly because the larger forms 

 grow on land where they are sub- 

 ject to rapid decay. So the record 

 of plant life in former geological 



FIG. 292. Gametophytes of the 

 quillwort (Isoetes) 



sperm. C, section of female game- 

 tophyte removed from megaspore, 

 showing sunken archegonium. A, 

 C, Isoetes echinospora. A, C, 

 after Campbell ; B, after Belajeff 



, . , A, male gametophyte within the mi- 

 ages IS poor as Compared With crospore: p, prothallial cell; four 



that of animal life. However, there s P erm mother cells shown within 



the reduced antheridium. B, 



are some very wonderful deposits 

 of plant remains forming the hard 

 and soft coal beds, which de- 

 serve brief mention here, since 

 most of the plants composing them are fossil pteridophytes. 

 During the Devonian and Carboniferous Ages the most con- 

 spicuous vegetation was represented by tree ferns and relatives 

 of the horsetails and club mosses, together with certain very 

 primitive gymnosperms. These plants reached the height of 

 trees and formed forests on the land and in the marshes (see 

 Plate VIII). The Calamites (Plate VIII, 2) were gigantic 



