390 MORPHOLOGY OF THE ANGIOSPERMS 



still apparent; the filament is somewhat flattened and shows weak 

 marginal growth.) Also shown in the family are stages in the change in 

 position of microsporangia from sunken to protuberant (Figs. 51 and 

 52 ) ; these are anatomical evidence tliat the anther sac represents remains 

 of the sporophyll lamina and that the sporangium has no sporangial 

 wall. Both Michelia and Talauma show stages in the evolutionary de- 

 velopment of the anther (Fig. 49). 



The gynoecium of Magnolia, with its greatly elongated receptacle 

 and closely placed, spiral carpels, is often cited as an example of the 

 primitive gynoecium, but that of Alichelia, with carpels laxly arranged 

 and distinct, is more primitive. In ovule number also. Magnolia is 

 more advanced than other genera in the family. Magnolia has the re- 

 duced number of two, Michelia has two to five, and Manglietia, three to 

 several. Similar extreme reduction in ovule number directly from 

 laminar, rather than from submarginal, placentation — the common 

 origin of solitary and paired ovules — is present in Nehtmbo, Cabomha, 

 and Brasenia (Fig. 85). Study should be made of the detailed vascular 

 supply of the carpel and ovules in Manglietia to establish more defi- 

 nitely the presence of laminar placentation in this line of woody 

 Ranales. 



The stamen traces in the family are commonly three, with five to 

 seven in species of several genera. Reduction in number to one is 

 clearly evident in both Magnolia and Michelia, where the lateral traces 

 show all stages of loss. (Most species of Michelia have only one trace.) 



The ovule traces have mixed origins — from placental vascular mesh- 

 work that is supplied by branches from both dorsal and ventral bundles 

 (Fig. 141). This origin of ovule supply represents modified laminar 

 placentation — reduction from a meshwork of connecting branches of 

 the dorsal and ventral bundles. It closely resembles that of Degeneria 

 and Drimtjs and is best seen in the closely related Michelia. 



The vascular structure of the floral axis is complex because of the 

 presence of a cylinder of cortical bundles, which join the stelar bun- 

 dles in supplying the floral appendages (Fig. 41). (There is no cortical 

 system in the vegetative axis, as in Calijcanthiis.) About twenty cortical 

 bundles arise from the axial stele in the middle of the peduncle, en- 

 large, and become concentric. At the base of the receptacle, they branch 

 and anastomose complexly, joining with the other higher branches from 

 the stele, then form a meshwork throughout the inner cortex of the 

 receptacle. The vascular supply to the appendages is insufficiently 

 known for the family as a whole, and it is perhaps not uniform. The 

 tepals seem to receive their supply wholly from the cortical bundles, 

 the stamens from a double — inner and outer — series of the upward- 

 continued cortical bundles. The median trace of tlie carpel is derived 



