278 MORPHOLOGY OF THE ANGIOSPERMS 



ovules is emphasized by the claim — by others than morphologists — 

 that some of the Sarcopodales are not angiosperms but belong in a 

 lower group, "prephanerogams," intermediate between gymnosperms 

 and angiosperms. (These plants have been shown to be true angio- 

 sperms, with reduced, not primitively naked ovules; the classification 

 of these taxa as prephanerogams was made on the invalid basis of a 

 single character, without regard to many otlier typical angiosperm 

 characters. ) 



All stages in extent of reduction are present in angiosperms, and the 

 less reduced types, with simplification of integuments and nucellus, are 

 common; the greatly reduced types, where the ovule body also is 

 strongly reduced, or even lost, and the archesporium lies in the pla- 

 centa or carpel wall (Figs. 106, 107, 108, and 109), are infrequent. The 

 less extreme modification is well illustrated by the related families, 

 Apocynaceae and Asclepiadaceae. In the Asclepiadaceae and the lower 

 tribes of the Apocynaceae, the nucellus is well developed; in the higher 

 genera, Vinca and Nerium, it is a single cell layer; in Apocijnum, it is 

 vestigial (Fig. 101). 



The minute ovules of Prosopanche ( Hydnoraceae ) are not as reduced 

 as they appear to be. The ovules appear as ovoid nodules in the pla- 

 centa, and minute projections appear above the surface (Fig. 108G); 

 in section, the nodules show typical ovule structure, a delicate integu- 

 ment and a thin, sheathing nucellus. The genus is unique in the sink- 

 ing of little-reduced ovules in the placenta; in other taxa, sunken ovules 

 are represented by archesporium only. The related Hijdnora has ovules 

 similar to those of Prosopanche on the surface of the placentae. 



The Santalales show many stages in the great reduction of the ovule. 

 In the Olacaceae, Anacalosa and Strombosia have ovules with simple, 

 thin integuments and thin nucelli; Olax has no integument, and its 

 nucellus consists of a few cells only. The Santalaceae are characterized 

 by a unilocular ovary which has a basal central column bearing distally 

 abortive ovules as lateral lobes or projections (Fig. 108E, F); the en- 

 tire placenta resembles the fruiting body of mushrooms (Fig. 107A to 

 E). The ovary seems to be syncarpous and inferior, having a reduced 

 free central placenta. The number of surviving ovules represented, as 

 indicated by the number of clusters of archesporial cells, is two to five 

 (Fig. 107A/). Details of placental structure are known in only a few of 

 the genera in the family. Comandra has ovules of anatropous form ( Fig. 

 107C), with remnants of a nucellus and integument. The ovules of 

 Santalum and Thcsitim are "outgrowths of the central column, pointing 

 downward" (Fig. 107A, B); in Osijris and Sclcropyrum, "the lobes point 

 upward" (Fig. 107E, F, G). Mijoschilos (Fig. 107N), Arjona, and 

 taxonomic descriptions of Quinchamalwn show that this peculiar plac- 



