A comparison of the taxonomic criteria employed for the higher animals and the higher plants respectively results in a striking contrast. Abundant use is made of skeletal characteristics in the classification of the Vertebrata, while such features are employed to a comparatively insignificant extent in the systematic grouping of the Vasculares. The value of the osseous skeleton of the higher animals in determining their affinities has been recognised since the beginning of the last century. It is only comparatively recently, on the other hand, that the fibro-vascular skeleton of the Vasculares has been discriminatingly used for phylogenetic purposes. The Brongniartian school of palæobotanists considered the possession of secondary woody growth to be an important indication of phænogamous relationship, and on this ground grouped the Calamites and Sigillarians with the Gymnosperms. A study of the very characteristic primary wood, as well as other less-important features in these two orders, led Williamson and his successors to put the Calamites with the Equisetales and the Sigillarians with the Lycopodiales. These conclusions have been fully confirmed by the subsequent discovery of typical heterospory in the two groups. The above examples will serve to illustrate the value of the primary fibrovascular skeleton from the phylogenetic standpoint. Palæobotanists have thus led the way in the proper taxonomic use of the fibrovascular skeleton; but from the very nature of their material they have not been able to any extent to use development as a phylogenetic key. Developmental studies which have been so fruitful in zoology have been almost entirely neglected by the Botanist in the case of the sporophyte of the various groups of the Vasculares. Here, again, we owe to a Palæohotanist the suggestion of the necessity of cultivating this field (D. H. Scott, ‘Presidential Address, Section K, Brit. Assoc.,’ 1896). A preliminary account of the writer's investigations on the development of the sporophyte was read by Professor Ramsay Wright at the May meeting of the Royal Society of Canada, 1896 (“A Theory of the Morphology of Stelar Structures,” ‘Proceedings of the Royal Society of Canada,' p. 106). A further abstract was published in 1897 (‘Report Brit. Assoc., Toronto,' 1897). On account of the extent of the subject and the difficulty of securing material of fossilized and tropical forms, it has been necessary to publish the work in parts. The first of these appeared in 1899, and was devoted to the Equisetaceæ (‘Boston Nat. Hist. Memoirs.' vol. 5, No. 5). The second, published in 1900, dealt with the Angiosperms (“Morphology of Central Cylinder in the Angiosperms,” ‘Canadian Inst. Trans.,' vol. 6).