402 MORPHOLOGY OF THE ANGIOSPERMS 



Although the ovules are borne in two rows, the placentation is 

 laminar, because the traces of the ovules are supplied by both the dorsal 

 and ventral bundles ( Fig. 83A, B ) . The majority of the proximal ovules 

 are supplied by bundles from the ventrals; the traces of some of the 

 distal ovules are branches from the dorsal bundles, and other ovules 

 receive traces from a meshwork formed by branches from both dorsal 

 and ventral veins. There is no constancy in the vascular plan of the 

 ovule supply, which is basically that of laminar placentation. 



There is only one archesporial cell, which becomes directly the 

 megaspore mother cell. The embryo sac is of the normal monosporic, 

 8-nucleate type. The young endosperm is cellular and, when mature, is 

 ruminate. The embryos are remarkable in their cotyledon number; three 

 are characteristic, four frequent. 



The long, abaxial microsporangia are deeply embedded in pairs be- 

 tween the major vascular bundles of the lamina (Fig. 67). The sporog- 

 enous tissue lies free in the mesophyll of the lamina; there is no spo- 

 rangium wall at any stage, but the epidermal cells directly over the 

 sporogenous tissue form a specialized thick-walled layer associated with 

 dehiscence. 



The nodes have five traces from five gaps. The vessels are scalariform 

 with many pores, thin-walled and angular in cross section; the pitting 

 of the side walls is also scalariform. The wood rays are narrowly multi- 

 seriate. The phloem consists of alternate layers of hard and soft cells. 



Like most other ranalian families, the Degeneriaceae show both 

 primitive and advanced characters. The leaves are like those of most 

 ranalian taxa — simple, pinnately veined. The flowers are solitary, but 

 the presence of two or three bracts along the flower stalk is perhaps 

 evidence that lateral flowers have been lost. The supra-axillary position 

 is probably not present in any other ranalian family. 



The perianth is highly specialized for a family primitive in many 

 characters; calyx and corolla are well differentiated, and their members 

 whorled. The multiseriate corolla is an example of the development of 

 the whorled arrangement before number of organs was reduced. 

 (Corollas with two whorls are present in Magnolia and Liriodendwn; 

 the Annonaceae show reduction from two whorls to one.) The stamens 

 and carpels are probably the most primitive in the order. The stamen 

 in its laminar form seems to be the most primitive known among 

 angiosperms. The sunken, wall-less microsporangia are doubtless the 

 primitive angiosperm type. (The Magnoliaceae show many stages in 

 the narrowing of the laminar sporophyll and the "freeing" of the 

 sunken sporangia.) The monocolpate pollen is one of the simplest in 

 angiosperms. 



In this family, reduction of the many carpels of typical ranalian fami- 

 lies to one is a prominent advanced character. Absence of fusion of the 



