SPERMATOPHYTA 



345 



phylls follows that of the leaves, lieing cyclic in the Cupressaceae and 

 spiral in the other families. 



Staminate Strobilus. In all the Coniferales the staminate strobilus is 

 simple, with few to many microsporophylls arising directly from the cone 

 axis (Fig. 295A). Bracts are not present. The stamen is a reduced 

 structure, generally consisting of a slender stalk and an expanded sterile 

 tip. The microsporangia are abaxial and most commonly borne in pairs 

 (Fig. 295^, C). Each stamen bears 

 2 microsporangia in the Abietaceae 

 and Podocarpaceae, 2 to 5 in the 

 Taxodiaceae, 2 to 6 in the Cupressa- 

 ceae, 6 to 15 in the Araucariaceae, 

 and 4 to 8 in the Taxaceae. In the 

 Araucariaceae and Taxaceae the mi- 

 crosporangia are pendent on a peltate 

 stamen, as in Ginkgo. The micro- 

 sporangia of conifers are eusporan- 

 giate, developing either from a single 

 hypodermal initial or from a layer of 

 initials. The wall is composed of 

 several layers of cells, the innermost 

 layer forming the tapetum. 



Ovulate Strobilus. A definite ovu- 

 late cone is present in all the families 

 of Coniferales except the Podocarpa- 

 ceae and Taxaceae, where it is greatly 

 reduced, in some of the Podocarpa- 

 ceae to one or two ovules and in most 

 of the Taxaceae to one. The ovulate strobilus differs from the staminate 

 in being compound, that is, the ovules are borne on secondary axes, as in 

 the Cordaitales. The main axis of the cone bears a number of bracts and 

 in the axil of each is an "ovuliferous scale" (Figs. 295i) and 296^). The 

 bract is homologous with the microsporophyll of the staminate cone, but 

 the nature of the scale is puzzling. The view most generally held is that it 

 represents a greatly reduced axillary shoot bearing a pair of leaves that are 

 fused along their margins. In fact, in abnormal cones the ovuliferous 

 scale is sometimes replaced by a spur shoot bearing two leaves. In the 

 Abietaceae the bract and scale are free, being united only at the base. 

 Although in the mature cone the bract is usually smaller than the scale 

 and inconspicuous, in some cases, as in Pseudotsuga and species of Larix 

 and Abies, it is large and very prominent. In the Taxodiaceae, Cupres- 

 saceae, and Araucariaceae the bract and scale are coalescent. 



In families having a well-developed ovulate strobilus, this nearly 



Fig. 295. Pinus nigra. A, longitudinal 

 section of staminate strobilus, each 

 microsporophyll bearing a pair of abaxial 

 microsporangia, X4; B, side view of a 

 microsporophyll, X 10; C, abaxial view of 

 same; D, ovuliferous scale, showing two 

 adaxial ovules, natural size. 



