THE AXGIOSPERMAE 1133 



the typically hermaphrodite flower, a gap which it is not easy to bridge, 

 either by theory or observation, so that the onus of proof that floral evolution 

 has in fact followed a course from the unisporangiate to the bisporangiate 

 condition still lies with its supporters. 



It is one of the characteristic features of the receptacle, in comparison 

 with a vegetative axis, that it has commonly no internodes. Cyclic flowers, 

 it is true, produce their parts in successive whorls, but they are generallv 

 not vertically separated and the plastochrone periods either overlap, so that 

 they cannot be distinguished, or perhaps disappear altogether. Neverthe- 

 less there are enough special cases known, in which internodes are part of 

 the floral architecture, to show that the plastochrone rhythm, though 

 disturbed, is not lost, at least in every flower. 



Elongation of the receptacle is of two kinds. There are the flowers in 

 which the receptacle is elongated throughout, even from its inception, as in 

 Magnolia, Myosurus, etc., and there are those in which the elongation of one 

 or more internodes only appears during development. The latter is a 

 fairly common phenomenon, though it does not always show itself in a 

 striking degree. (See also p. 1139.) 



An expansion of the receptacle either within the calyx or within the 

 corolla is sometimes known as the disc. This is not necessarily an elonga- 

 tion and is more often a lateral expansion, which may or may not take the 

 form of a disc in the ordinary sense of the word, interpolating a naked zone 

 between perianth and stamens or between the gynoecium and the other 

 floral parts, as in the Strawberry and other slightly perigynous flowers. 

 In Priimis and Rhammis, for example, the disc is cup-shaped and this is 

 often interpreted as a stage in the evolution of highly perigynous and epi- 

 gynous flowers. The term disc is however also applied to the naked zone on 

 top of the gynoecium in epigynous flowers, e.g., in Umbelliferae, where it 

 surrounds the stvle and extends to the androecium, in which case it is not 

 obviously or certainly a part of the receptacle. The disc is often associated 

 with the production of nectaries and sometimes its whole surface may be 

 secretory. It is true that the apparent expansion of the receptacle into a 

 disc or cup may be interpreted, we shall see below, as a structure formed 

 of the fused basal parts of the perianth or the androecium or of both, but 

 in other cases there are grounds for the belief that a toral enlargement has 

 occurred. For example in certain sections of the family Monimiaceae 

 typified by the genus Tamhoitrissa (Fig. 1 106), the flower takes the form of 

 a flattened, hollow vessel of fleshy consistency, with only a small opening 

 above, all over the inside of which the carpels stand immersed in the 

 fleshy tissue. This does not bear the aspect of a combination of organs, but 

 rather that of a genuine receptacular cupule. 



This latter structure, the cupule, is seen at its best development in the 

 order formerlv called the Cupuliferae and now known as Fagales. The 

 traditional view of the cupule which surrounds the fruits in Overciis, Fagiis, 

 Castanea, etc., is that it is formed of a number of fused bracts, which in the 

 two latter genera separate at maturity into four woody valves. There is 



