FOSSIL PLANTS 



339 



B 



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

 stored in the megaspore, as in Marsilia and Selaginella. 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 -hi story p 

 formula is the same as that of Sel- 

 aginella (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 

 <4row on land where they are sub- 



ject to rapid decav. So the record FlG - 292 ' Gametophytes of the 



| . 1-1 uillwort Isoetes 



of plant life in former geological 



^1, male gametophyte within the mi- 

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



sperm mother cells shown within 

 the reduced anther id ium. />, 

 sperm. C, section of female game- 



that of animal life. However, there 



are Some very wonderful deposits 



of plant remains forming the hard ^phyte r e m ved f rom megaspore, 



showing sunken archegouium. .1 , 



and soft coal beds, which d e- c, Isoetes ech inospom .--A, (.', 

 serve brief mention here, since after Campbell ; U; after BelajefE 



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 ('l<mnte.s (Plate VIII, 2) were gigantic 



