Vascular Anatomy of the Megasporophylls of Conifers

Abstract

1. In the evolution of the ovulate strobilus in members of the Coniferales, two general tendencies are apparent: (1) the reduction in number of sporophylls in the strobilus; (2) the modification of a compound sporophyll into an apparently simple sporophyll; the latter appears in diverse disguises, but in general implies loss of one of the sporophyll members or welding of the two. 2. Strobilus reduction has reached its highest expression in members of the Cupressineae, Taxineae, and Podocarpineae; one type of strobilus reduction is represented by the general sterilization and reduction of parts in the lower sporophylls of Pinus. 3. Simplification of a compound sporophyll has been attained to fullest extent in Arthrotaxis selaginoides, Agathis, and Saxegothaea, and possibly others; an extensive reduction of bract occurs in Cedrus Libani and the lower sporophylls of Pinus maritima; the scale in Phyllocladus is probably reduced so as to be represented only by a distinct ovular supply; the welding of the two organs is complete in Juniperus communis and Chamaecyparis Lawsoniana. 4. Fusion of bract and scale vascular supplies does not directly parallel fusion of bract and scale. 5. Separate origin of bract and scale vascular supplies occurs most generally in the Podocarpineae and Abietineae; fusion of bract and scale supplies has reached its highest expression in the Araucarineae; both types of bundle origin are represented in the same strobilus in Cryptomeria japonica, Cupressus Benthamii, and the lower sporophylls of Pinus. 6. The bract bundle in plants with uninerved vegetative leaves divides only slightly if at all; the extent of the scale bundle system is directly related to the size of the organ supplied. 7. The scale bundles in the Abietineae and Chamaecyparis Lawsoniana form in the expanded portion of the organ a straight row or arc; in members of the Taxodineae and Cupressineae scale bundles swing around so as to lie at each side of the bract bundle. 8. In Cryptomeria japonica and Cupressus Benthamii and perhaps Cunninghamia Davidiana scale bundles accompany the bract bundle into the free portion of the bract. 9. A branching bundle in the vegetative leaf in Araucaria and Agathis probably implies a branching bundle in the bract of the sporophyll; the vascular system in the megasporophyll is probably a complex of bract and scale bundles. 10. In species of Podocarpus the scale bundles continue in the portion of the scale folded toward the dorsal side, forming the epimatium of the ovule.