CONIFEROUS PLANTS. 



167 



This is peculiarly the case with the coniferce, which form 

 a large and very important tribe among living plants. They 

 are characterised not only by peculiarities in their fructifica- 

 tion, having, together with the cycadea, their seeds originally 







PIG. 107. 



FIG. 108. 



naked, and not enclosed in an ovary, for which reason they 

 have been arranged as a distinct order ; but they are still 

 farther distinguished by the peculiarity of their woody 

 structure, whereby the smallest fragment can readily be 

 identified. A transverse section of any coniferous wood, in 

 addition to the radiating and concentric lines, exhibits a 

 system of reticulations by which coniferce are distinguishable 

 from other plants. The cross lines a, a, indicate the annual 

 circles of growth (fig. 108). 



Among other characteristics of trees of this order, they 

 all secrete resin, have branched trunks, and linear, entire, 

 rigid leaves, and they occur both in the hottest and coldest 

 regions. It should be observed that the minute structure 

 of wood above described can only be studied by the aid o 

 the microscope. 



INVESTIGATION or FOSSIL PLANTS. The object chiefly 

 desired by the student of fossil botany, is to acquire such a 

 degree of knowledge as will enable him to determine a 

 fossil plant with facility and correctness, and to refer it to 

 the genus and species to which, if already known, it 

 belongs. The remarks of Dr. Lindley and M. Brongniart 

 on these points are so important and instructive, that we 

 have transferred to our pages the substance of their 

 observations. 



