PALEOBOTANY BERRY. 369 



the nutriment for the developing embryo and the subsequent 

 germinating plantlet. This course of events is strikingly uniform 

 throughout the phylum and is unknown in other plants. 



Those who consider the formation of seeds as the most important 

 characteristic of a definite group of vascular plants (Spermophyta) 

 ignore the history of the origin of the seed habit, and the result is 

 no more natural than the old Exogenous and Endogenous classes, 

 or than one which attempted to use homospory and heterospory to 

 define natural groups of the remaining vascular plants. Moreover, 

 such a treatment is confronted with the necessity of defining a 

 flower. If a flower is considered as a group of sporophylls in order 

 to include the gymnosperms, it then includes many of the so-called 

 flowerless plants. If, on the other hand, the gymnosperms are 

 placed in their correct perspective and a flower is defined as a group 

 of sporophylls associated with a perianth, the limit of the flower 

 corresponds almost exactly with the limits of the phylum (except 

 Gnetales) and the necessity, if such exists, for abandoning the con- 

 venient term flowering plants, as some students have advocated, is 

 obviated. The popular concept of a flower is too firmly intrenched 

 to warrant any attempt to arrive at a more philosophical morphol- 

 ogy, and the fact that floral envelopes are lacking, either primitively 

 or by reduction in some groups, is no more pertinent than the fact 

 that some flowers consist entirely of floral envelopes and lack sporo- 

 phylls. 



The presence of floral leaves (calyx and corolla) surrounding the 

 sporophylls and derived both from sterilized sporophylls above and 

 bracts below, appears to have been conditioned largely by the habit 

 of entomophily. Although the primitive floral envelopes were 

 probably protective in their function, certainly their subsequent 

 history and great diversity of detail are the result of entomophily. 

 In the more primitive flowers the sporophylls tend to be free and 

 the axis tends to be elongated with the members in a spiral arrange- 

 ment. Evolution of the flower proceeded along the lines of reduc- 

 tion in axial length until the members passed to a cyclic arrange- 

 ment when they tended to become definite and fewer in number and 

 at length became confluent to a greater or less degree. The three 

 marked stages are termed hypogynous, perigynous and epigynous, 

 and all grades of intermediate stages are present. Inequalities of 

 growth result in other diversities. The members tend to evolve 

 from a radial symmetry (actinomorphic) to a bilateral symmetry 

 (zygomorphic) or to an isobilateral symmetry with two planes of 

 symmetry and with the halves unlike. 



Systematists segregate angiosperms into two series — monocotyle- 

 dons and dicotyledons — and there has been almost endless discussion 

 as to which line was the more primitive. Both were present in the 



