FOSSIL PLANTS OF THE CARBONIFEROUS SYSTEM. 



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cone-like fruit is said to occur in a fossil form called Lepidostrobus ; 

 but under this name, as well as that of Strobilites, the fruit of many 

 different plants seems to be included. Lepidophyllum is said to be 

 the leaf of some Lepidodendron, and Ulodendron is an allied genus. 



1182. Stigmaria (oriypa., a mark or impression) is a fossil genus, 

 the species of which abound in the coal measures. They occur generally 

 in the bed called the Underclay. Stigmaria ficoides (fig. 802) is the 

 common species. It consists of a dome-shaped mass sending forth 

 grooved and pitted branches, which divide dichotomously, and extend 

 20 to 30 feet. Slender processes are given off, which appear to have 

 been hollow (fig. 802). These processes (called fistular leaves,) form 

 an en.-oigled mass traversing the argillaceous lower bed in every direc- 

 tion. In Stigmarias three tissues are met with, vascular tissue forming 

 the inner part of the cylinder, ligneous forming the wood, and cellular 

 tissue forming a broad cortical zone, as well as the central portion or 

 pith. Some think that the stores of fossil fuel in England and America, 

 are mainly due to the presence of this plant. There are no plants of 

 the present day which resemble Stigmarias. Some have referred 

 them to such genera as Cactus and Euphorbia, others to Isoetes. 

 King says that they are the roots of the fossil plants called Sigillaria. 



1183. Sigillaria (sigillum, a seal) is another plant which appears 

 to have aided in the formation of coal. It occurs in the form of com- 

 pressed stems, attaining a height of 40 to 50 feet, and a breadth of 5 

 feet. The stems are fluted longitudinally, and marked at regular 

 intervals by single or double scars, the remains of the leaf insertions 

 (fig. 803). Some suppose Sigillarias to be allied to Tree-ferns, others 



Fig. 802. Stigmaria ficoides; a branch giving off flstulav leaves, which traverse the Underclay 

 "' Fig. 803. Sigillaria pachyderma: the stem marked with scars, and fluted longitudinally. 



