414 MORPHOLOGY OF GYMNOSPERMS 



sperms, for that condition doubtless appeared independently several 

 times, just as the monosporangiate strobilus is known to have appeared 

 at least twice in distinct phyla (coniferophytes and cycadophytes). 



Another fact in reference to the strobili of Cordaitales, which must 

 stand for the most ancient gymnosperm strobili, is that they included 

 both simple and compound strobili. The staminate strobilus was 

 simple, that is, its sporophylls were borne directly upon the axis of 

 the strobilus; and this type of staminate strobilus persisted through- 

 out the Ginkgoales a.nd Coniferales. Among the Gnetales the stami- 

 nate strobilus is compound, the individual simple strobili being borne 

 on axes of the second order in the axils of sterile bracts which make up 

 the general strobilus. There is an evident relationship between the 

 compact compound staminate strobilus, such as occurs in Ephedra 

 and in Welwitschia, and the short foliage branch bearing axillary 

 simple staminate strobili, as in Torreya. Even in Gnetiim the com- 

 pound staminate strobilus is a loose one; and among the taxads there 

 is a tendency to compact the staminate strobiliferous branch. The 

 conclusion is that the staminate strobilus is quite persistently simple, 

 but that in the more modern members of the phylum it tends to become 

 compound, a condition accomplished by compacting a short strobilif- 

 erous shoot. 



The ovulate strobilus of Cordaitales was compound, at least in 

 the very few specimens sectioned; that is, the ovules were borne on 

 short secondary and bractlet-bearing axes that arose in the axils of 

 the sterile and overlapping bracts that constituted the strobilus. 

 This compound ovulate strobilus is a distinctive feature of the Conif- 

 erophytes, prevailing among the Pinaceae and characterizing the 

 Gnetales. That simple ovulate strobili may have been derived from 

 it is quite possible. For example, in Torreya the ovulate strobili 

 are simple and are axillary on short leafy branches, just such a branch 

 as could have arisen through the elongation of the axis of a compound 

 ovulate strobilus, so that the sterile bracts could be replaced by foliage 

 leaves. It may be said that the change may have taken place in the 

 other direction, and that the short leafy strobiliferous branch was 

 compacted into a compound ovulate strobilus ; but it must be remem- 

 bered that the Cordaitales with their compound ovulate strobili are 

 very old, and that the Taxineae with their leafy strobiliferous branches 



