FOSSIL GYMXOSPERMS 



149 



part of the strobilus. The two distinct ovules show that they 

 are young by the fact that their stalks have not elongated. 



The monoecious habit among Gymnosperms is not unusual, 

 although it has never been found among Cycads; but that this 

 habit should take the form of a bisporangiate strobilus is espe- 

 cially interesting. Such strobili are found occasionally among 

 Conifers, but they are regarded as abnormal (Fig. 59). To 

 discuss the significance of these bisporangiate strobili seems to 

 us premature at present, since the results thus far announced 

 are very meager as compared 

 with those we have a right to 

 expect. It may be well, how- 

 ever, to make the following 

 statements. That a bispo- 

 rangiate strobilus must have 

 existed at some time among 

 the ancestral forms of Gym- 

 nosperms has already been in- 

 dicated by Tumboa, in which 

 the association of the two 

 forms of sporangia is more 

 intimate than in Cycadeoidea. 

 It seems evident, also, that a 

 bisporangiate strobilus holds 

 no more relation to an angio- 

 spermous "flower" than does 

 a monosporangiate strobilus; 

 and that neither type of stro- 

 bilus among Gymnosperms is 

 related to the angiospermous 

 flower in any way. Whether 

 a bisporangiate or a monosporangiate strobilus is the more 

 primitive is a question that probably finds its answer in the 

 statement that both conditions exist in the most primitive 

 forms. In Bennettitales, therefore, we are discovering inter- 

 esting transitions between Pteridophytes and living Gymno- 

 sperms, but there is not as much suggestion of Angiosperms as 

 the living Gymnosperms have already given. 



While the characters of Bennettitales justify the belief that 

 they must be closely associated with Cycadales, the axillary 



t 



FIG. 105. Cycadeoidea colossalis, transverse 

 section through the central region of a 

 very young strobilus, showing the axis- 

 bearing stalked ovules and interseminal 

 scales, x 10. From preparation made by 

 G. R. WIELAND from specimen in Yale 

 University Museum. 



