Scrophulariaceae and Orobanchaceae 167 



mis or exothecial tissues become increasingly thickened on their 

 outer and lateral walls in u-shaped manner until toward the tip 

 of each awn the thickening may be almost as deep as the cell 

 cavity. Transverse and longitudinal sections of the awns of 

 Aphyllon are figured in Plate XV, Figs. 29, 30. 



Were the above not a continuous morphological series from 

 green to degraded parasitic plants, one can scarcely suppose 

 that such similarities and histological details could have evolved 

 in two such related families. 



Pistil 



In a study of the pistil the fundamental point for consider- 

 ation is the supposed invariable two-celled ovary in Scrophulari- 

 aceae and the one-celled ovary in Orobanchaceae and Gesner- 

 aceae. This has already been discussed generally on pages 6-8. 

 The varying structural details from a two- to one-celled con- 

 dition, as well as the diverse views expressed as to the affinities 

 of such genera as Hyobanche, Lathraea, Christisonia that show 

 wavering transition from two- to one-celled states, emphasize 

 again the fact that here we are dealing with a condensing and 

 simplifying variation. No such transition-relations are even 

 suggested between Gesneraceae and Orobanchaceae. 



In the different genera of the Orobanchaceae the fused mar- 

 gins of the carpels grow inward to a varying degree from shallow 

 marginal placentas to deep parietal, that approach central pla- 

 centation. So the fundamental point of supposed affinities be- 

 tween Gesneraceae and Orobanchaceae entirely breaks down, 

 while a natural and continuous affinity between degraded par- 

 asitic Scrophulariaceae and still more degraded Orobanchaceae 

 has been established. 



Hairs of the Pistil 



The presence of hairs on the style and ovary in the different 

 genera of the two families is not a constant feature. They differ 

 as to number, distribution, and type. The following results 

 were noted: 



In Gerardia aspera the hairs on the style, though present, are 

 few in number. 



In species of Odontites the base of the style and upper part 

 of the ovary are very hairy, while the upper part of the style is 

 almost glabrous. The hairs are long, narrow and pointed. 



