BENNETTITALES 85 



recognizable, except to one very familiar with the situation; and there 

 may be many sections that would not show any trace of it. The 

 obliteration of the suspensor would be even more extreme in the case 

 of an embryo that has completely or approximately obliterated all 

 the tissues within the testa. At the same time, the embryo of Ginkgo 

 suggests the possibility that the embryo of Bennettitales may have 

 lacked an elongated and slender suspensor, and that there was simply 

 a suspensor-like elongation of the massive proembryo. In certain 

 sections Wieland (20) has discovered the seed filled with a tissue 

 which suggested to him proembryonic tissue. It is altogether unlikely 

 that the embryo in its proembryonic stage would have destroyed all 

 the endosperm. The tissue in question is probably that of the embryo, 

 through which both transverse and longitudinal sections are possible 

 that would not show the dicotyledonous character, or the figure 

 published might indicate three cotyledons. 



It is tempting to cite the embryo of Bennettitales as evidence that 

 the primitive embryo of gymnosperms was dicotyledonous. Recent 

 investigations, however, have shown that Bennettitales cannot be 

 used for or against this view until the anatomical structure of its cotyle- 

 dons has been determined. The embryo of this group, as we know 

 it, is probably far from representing even the most primitive embryo of 

 mesozoic gymnosperms; and behind the Mesozoic there stretches the 

 long series of paleozoic Cycadofilicales, whose embryos are unknown. 



5. History and distribution 



This characteristic mesozoic type ranges from the early Triassic 

 into the Lower Cretaceous, being extraordinarily abundant during 

 the Jurassic. In the United States the remains of Bennettitales are 

 known from the Triassic of Pennsylvania and North Carolina, through 

 the Jurassic of Colorado and the Potomac formation of Maryland, 

 to the Upper Jurassic and Lower Cretaceous of the Black Hills of 

 South Dakota and Wyoming. The recently discovered Mexican 

 remains of the group occur in the Lower Jurassic (Lias) of the moun- 

 tains of western Oaxaca (30). The known historical range of the 

 group in Europe is even greater, beginning with the early Triassic 

 (Williamsonia angiistijolia) of southern Sweden. 



The remains have been found in abundance wherever favorable 



