185 



Order CONIFERS. 



Stem much branched, leaves usually small and simple. Flowers 

 unisexual and without a perianth, plants monoecious or dioecious. 



The past history of the Conifer at is but imperfectly known, and, 

 owing to peculiar difficulties connected with the determination of 

 fossil forms, the evidence of palasobotany as to the development 

 and geological distribution of these plants, must be accepted with 

 the greatest caution. It would take us far beyond the limits of 

 the present work to discuss at length the distribution in time of 

 coniferous types. In the Palaeozoic rocks there are various repre- 

 sentatives of this Class, and we have an example, in such an 

 extinct genus as Cordaites, of a synthetic type in which coniferous 

 characteristics are combined with certain structural features met 

 with in other Orders of gymnosperms. As a general rule, fossil 

 conifers are perhaps the most unsatisfactory plants with which the 

 palseobotanist has to deal : structureless and imperfectly preserved 

 fragments of broken twigs, isolated cones, leaves or seeds, have 

 usually to be determined separately, and it is only in comparatively 

 rare instances that we are in a position to connect cones and vege- 

 tative branches. Coniferous wood, with its mineralized tissues more 

 or less well defined, is met with in rocks of nearly every age, 

 but here, again, the stems or thick branches must be determined as 

 far as possible from histological structure alone, and without any 

 leafy twigs or reproductive organs. Goppert, 1 Kraus, 1 KLeeberg, 1 

 Felix, 1 Schenk, 2 Knowlton, 3 and others have attempted to devise 

 convenient methods of classifying and identifying fossil Coniferte by 

 means of the peculiarities of structure presented by the secondary 

 wood and the distribution of resin ducts. For the most part, 

 however, fossil conifers are represented by structureless casts or 

 impressions of leafy branches, occasionally bearing characteristic 

 cones or other forms of reproductive organs. 



In treating of the Cycadacea, some general account was attempted 

 of the difficulties and possible sources of error which ought to be 



1 For references see Solms-Laubach's Fossil Botany. 



2 Zittel (A.), Handbuch, p. 848. 



3 Knowlton (A. 2), Bull. U.S. Geol. Surv. No. 56, 1889. (See also Goppert 

 and Menge, Die Flora des Bernsteins, vol. i., and Conwentz.) 



