From the Preface.
In 1901 our Morphology of Spermatophytes, Part I, was published, which comprised a presentation of the gymnosperms. It had grown out of a special course given to graduate students for several successive years, and although most of the ground had been traversed in this way several times, the larger part of the material in the book was taken from the contributions of other investigators. There was some new material included, but the chief contributions of the book were certain illustrations and the organized presentation of the group as a whole for research students.
During the last decade the special course referred to has been continued for successive generations of graduate students, with a constantly widening range of material and from new points of view. In addition to this extensive and repeated critical examination of material, a number of special investigations have been carried on in the laboratory. These investigations have been planned so that there might be not only a research contact with all regions of the gymnosperm series, but also a clearing up of unknown or doubtful forms. These special contributions from the laboratory have aggregated twenty-six since 1901, and have dealt with fourteen genera, distributed as follows: in Cycadales, Dioon, Microcycas, Encephalartos, Ceratozamia, and Zamia; in Ginkgoales, Ginkgo; in Coniferales, Pinus, Thuja, Torreya, Phyllocladus, Podocarpus, and Dacrydium; in Gnetales, Ephedra and Gnetum. This has enabled us to present the living groups from an entirely different standpoint, and to use many illustrations prepared in this laboratory. The present account, therefore, is based upon our own work, supplemented by the work of other investigators, rather than a compilation from literature, supplemented by occasional personal observations.
Furthermore, the last decade has been one of unprecedented activity in the investigation of gymnosperms, as a comparison of the bibliography of the volume of 1901 with that of the present one will indicate. In this period the number of titles has increased from 112 to 420, some of the additions being accounted for by the larger inclusion of paleobotanical material. Aside from a far more complete knowledge of the living groups, including as it does now at least the salient facts in reference to almost every genus, there have been two notable advances. In the first place, during this period vascular anatomy has developed as a subject of first importance, and some of its most conspicuous contributions have been in connection with the origin and relationships of gymnosperms. In the second place, paleobotany has brought to light during the last decade more facts of importance in reference to the history of gymnosperms than in reference to any other group of plants. This has enabled us to treat of the extinct groups in a way that was impossible ten years ago...