326 IOWA ACADEMY OF SCIENCE Vol. XXV, 191S 



lateral branches; stem ^een with irregular greenish pratuber- 

 anees and conspieuons alternate wartlike projections. First, sec- 

 ond, third and fourth leaves pinnately compound, each with 

 eight elliptical to ovate, entire leaflets. Leaves alternate ; petiole 

 at base swollen, upper surface of petiole slightly hollowed length- 

 wise; leaves distinctly reticulately veined, ciliate on margin, 

 upper surface smooth, a few scattered hairs. Petiole and petio- 

 lules pubescent. At axils of buds are small buds. No stipules, 

 but a slight prominence. Trichomes numerous on margin of the 

 leaf, occurring singly, curved, cell wall thin, surface roughened. 



Fig. 97 Fig. 98 



Fig. 97. — Trichomes of Gymnocladus dioica; a, showing strife on surface. 

 Drawn by C. M. King. 



Fig. 98. — Trichomes on margin of leaf of Ptelea trifoliata. Drawn by C. 

 M. King. 



RUTACE^. 



Ptelea trifoliata L, Hop Tree. Shrubby Trefoil. Germina- 

 tion about 5 per cent in greenhouse, epigaeous; stem pubescent, 

 hairs turned back and glandular; cotyledons 10 to 15 mm. long, 

 5 to 7 mm. broad, finely crenulate ; petiole pubescent beneath. 

 Leaves opposite, first pair with three fully formed leaflets, smooth, 

 slightly hairy on mid vein. Third petiole greenish or purple. 

 Bud in axil of the leaf. Sargent^^ gives notes on the seeds and 

 germination of Ptelea trifoliata. Trichomes comparatively color- 

 less, short, curved, pointed to blunt, walls roughened, thin, base 

 enlarged. Secretion receptacles occur on the young leaves. In 

 early stages the center of the receptacle is green. Trichomes of 

 cotyledon upper surface, short, curved, one-celled, pointed, walls 

 thin; nuclei often distinct. Glandular trichomes less frequent 

 than simple trichomes. 



SAPINDALES 

 The germination of the seeds of this family is variable, in 

 some cases epigceous, in a few cases hypogaeous. Most of the 

 seeds require a period of rest; a notable exception, however, is 



-^Silva of North America, 1, pp. 76-77. 



