SPERMATOCYTES 181 



A. GYMNOSPERMS 



This group includes the primitive seed plants, and to understand their 

 relation to pteridophytes it will he necessary to consider them in their 

 historical sequence. Seven great groups are recognized: (i) Cycado- 

 Jilicales, (2) Bcnnettitales, (3) Cycadales, (4) Cordaitales, (5) Ginkgoales, 

 (6) Coniferales, and (7) Gnetales. The first, second, and fourth of these 

 groups are extinct. 



(1) Cycadofilicales 



Discovery. — The discovery of the existence of this most primitive 

 group of seed plants, known only in the Paleozoic and chiefly in the 

 Carboniferous, is so recent that a brief outline will be of interest. The 

 Coal-measure deposits are notable for the remains of fernlike plants, 

 and such plants constitute about one half of the known vegetation of the 

 time. Until recently all of these plants were thought to be ferns, the 

 evidence from their leaf forms and venation appearing to be conclusive. 

 Most of them show no sporangia, and such sporangia as do appear are 

 mostly of the Marattia type. The first expressed doubt (1883) that these 

 fernlike plants were all ferns arose from the persistent absence of spo- 

 rangia. Later the anatomy of the stems of several forms was discovered 

 to show characters combining those of ferns and of cycads, and for such 

 forms the group name Cycadofilices was proposed (1899). In 1903 

 seeds were found on the leaves of certain of these Cycadofilices, and the 

 group name Pteridos perms was proposed to include the Cycadofilices 

 that bear seeds. Finally, in 1905 the microsporangia were discovered; 

 and curiously enough some of these microsporangia were the sporangia 

 of so-called ferns. Therefore, a knowledge of the existence of ferns dur- 

 ing the Carboniferous came to depend more upon inference than upon 

 any sure recognition of their remains. In any event, it seems certain 

 that almost all of the so-called fern vegetation of the Carboniferous be- 

 longs to these primitive seed plants. The oldest name for the group is 

 here adopted, its termination being adapted to that of the other groups 

 with which it is coordinate. 



Sporophyte. — The habit of the sporophyte body is conspicuously 

 fernlike, including not merely the usual fern habit, but also climbers and 

 trees. The vascular anatomy, which first separated the group from 

 ferns, deserves brief mention. Three of the four conspicuous typos of 

 vascular cylinder found among ferns (see p. 156) are found in the stems 

 of Cycadofilicales, the three representative genera illustrating them be- 



