12 MORPHOLOGY OF AXGIOSPERMS 



series " comprising all those families that show the spiral tend- 

 ency in any of the floral sets, and the " cyclic series " compris- 

 ing all those whose flowers are completely cyclic, the former 

 series including all the more primitive families. There is no 

 reason why this same distinction can not be applied also in a 

 general way to the Archichlamydeae. This gradual transition 

 of flowers from the spiral to the cyclic condition is one of the 

 best-marked tendencies in their evolution, and has the advan- 

 tage of being represented by innumerable intermediate stages. 

 All of those families which are recognized as being of the high- 

 est rank have completely cyclic flowers, with members appearing 

 in definite and low numbers, notablv illustrated bv the whole 

 group Sympetalae. 



There is a marked tendency in flowers for the members 

 of a single set to lose their identity and to develop en masse, 

 a phenomenon called " coalescence " by the older morphologists, 

 under the impression that separate members had united. This 

 congenital union is to be distinguished from such a mechanical 

 union as is shown by the anthers of Compositae. In the organ- 

 ogeny of such a flower it is to be observed that in the meriste- 

 matic zone from which a certain set is to develop, the different 

 members first appear as separate primordia, but sooner or later 

 the whole zone shares in the growth and, the axial growing 

 point being checked, an annular structure arises that gradually 

 assumes the size and form of the mature organ (Fio-. 1). It 

 has been claimed that this is a toral uprising and that, for 

 example, the tubular portion of "a sympetalous corolla is mor- 

 phologically torus, but there seems no more reason for this 

 supposition than to regard an individual petal as a toral up- 

 rising. It is merely the difference between development from 

 the meristematic zone at certain points and at all points. As 

 is well known, this development of the whole zone may begin 

 almost at once, or may be deferred until the set is nearly mature, 

 resulting in every stage of separation in the members, from a 

 completely tubular structure to one that is tubular only at base. 

 Or the zone may develop for a time in two sections and later 

 en 7nasse, resulting in the so-called bilabiate structure. Further 

 inequalities in the time and rate of development result in 

 various irregularities. In any event, this tendency to zonal 

 development rather than the maintenance of separate points of 



