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A TEXTBOOK OF THEORETICAL BOTANY 



maintained the primitive non-strobilate arrangement of the reproductive 

 structures which characterizes the Ferns. The close proximity of female 

 gametophytes in a strobilus obviously increased the chances of fertilization 

 for each of them, and this type of arrangement offered possibilities of evolution 

 into the flowers of to-day, while the handicap of their less efficient organization 

 brought the Pteridosperms to early extinction. 



The Cordaitales themselves probably did not give rise to the modern 



Fig. 650. — Cordaites penjoni. 

 Longitudinal section of a 

 microsporangiate cone. 



{After Renault.) 



Fig. 651. — Cordaites idUiamsoni. 

 Longitudinal section of a 

 niegasporangiate cone with 

 seeds. {After Renault.) 



Flowering Plants, though they may have survived into Mesozoic times. The 

 ancestral fern-like complex, however, evolved along several diflferent lines 

 and another strobiloid offshoot, the Cycadales, has survived to the present 

 day, and appears to be at least related to the forerunners of the Angiosperms. 



The lowest group of the Flowering Plants is therefore that in which seeds 

 are borne uncovered on sporophylls arranged in a strobilus or cone, and 

 this group is called the Gymnospermae or naked-seeded plants. 



We will only note in passing that they are almost all trees, and that the 

 development of secondary xylem, of which we have seen only traces in the 

 lower groups, has, with the adoption of the seed-habit, been increased to an 

 enormous extent, so that these plants build up in the course of vears large 

 woody trunks like those of the Pine and the Yew. 



