THE MEGASPORANGIUM 



55 



Integuments. Ordinarily the ovule has either one or two integu- 

 ments. The number is constant in most families, and only in rare 

 cases do unitegmic and bitegmic ovules occur in the same family. 

 In the Sympetalae a single massive integument is almost universal, 



ABC D E 



Fig. 37. Types of ovules as seen in vertical longitudinal section. A, atropous or 

 orthotropous. B, anatropous. C, campy] otropous. D, hemianatropous. E, am- 

 phitropous. (After Prantl.) 



the Plumbaginales and Primulales being the only important excep- 

 tions. In the Archichlamydeae and the monocotyledons most gen- 

 era have two integuments but a few have only one. There is 

 evidence that in many cases the single integument has originated 



C ~ v D E F 



Fig. 38. Development of ovule of Plumbago capensis. (After Haupt, 1934-) 



by a fusion of two separate primordia. Transitional types have 

 been observed in some members of the Ranunculaceae, Rosaceae, 

 Connaraceae, and Icacinaceae. 



The unitegmic condition may also arise by an elimination of one 



