On the Affinities of Certain Anomalous Dicotyledons

Abstract

THERE is still a difference of opinion among botanists as to the relationship between the two great divisions of angiospermous plants, monocotyledons and clicotyledons. The two groups have evidently been derived from a common stock, but which branch is the older is still somewhat doubtful. Among the genera commonly referred to the dicotyledons are several which differ from the typical forms both in the structure of the flowers and in the character of the tissues, especially the structure and distribution of the vascular bundles. Among these anomalous dicotyledons may be mentioned the Nymphzeacme, certain Ranunculaceme (Act-ea, Thalictrum), and among the Berberidaceme, Podophyllum, Diphylleia, and Caulophyllum. A recent paper I on the embryo of Nelumbo has called attention to the importance of a thorough study of these anomalous genera, whose embryogeny is almost completely unknown. The result of Lyon's examination of Nelumbo was the discovery that the apparently dicotyledonous embryo has really but a single cotyledon and resembles that of the aquatic Alismales, an order of monocotyledons that shows numerous analogies with the Nymphmeace. This interesting discovery suggested to the writer the advisability of looking up what had been already done with the study of the embryos of some of the other forms referred to, and although the results of these inquiries have been very incomplete, they have revealed a number of extremely suggestive facts, which are here given, and which emphasize the desirability of more thorough work in the same direction.