318 IOWA ACADEMY OF SCIENCE Vol. XXV, 191S 



wall fairly thick. Smaller trichonios sliort, slender, pointed, 

 roughened, prickle-like in appearance. Dentations of leaf tipped 

 with fflandnlar teeth. 



Fig. 82. — Trichomes from seedling leaf of Pyrus malus. Drawn by C M. 

 King. 



ROSACEA 



Sa.chs-° figiired the germination and seedling's of Prumis Cera- 

 siis and Amygdalus communis. Lubbock-^ notes that the seed- 

 lings show a great similarity amongst the cotyledons of different 

 species and genera. In one type the embryo is amygdaloid, the 

 cotyledons are nearly all of the same outline, the petiole is short.. 

 In another type the cotyledons are emarginate, in a third form 

 they are cordate. Of the trees Lubbock-- studied Pyrus Aucu 

 patia Gaertn, Crataegus oxijcantha L.. C. Mexicana D. C. 



Pyrus malus L. Apple, cultivated, source unknown. Germina- 

 tion epiga^ous, stem purplish above, white below, cotyledons 

 tleshly, nearly obcordate, sessile, both surfaces smooth, slightly 

 tapering at the base. Subsequent leave.s alternate, stem purplish, 

 pubescent. First leaves serrate, prominently veined above ami 

 below, smooth above and below. Third leaf with prominent den- 

 tate stipules; petiole smooth, prominently pinnately veined, 

 smooth above and below. Fourth leaf smooth above and below, 

 prominently veined, hairs on midrib. Trichomes loug, slender, 

 gradually tapering, inclined to Ije tloecose; wall at point thick- 

 ened, somewliat blunt, of medium thickness, colorless. 



Crataegus mollis (T. and G.) Scheele. Fruit collected at Cen- 

 terville, Iowa, September 28, 1917. Seeds planted in stratifying 

 bed October 10; removed to greenhouse March 14. Germinated 

 April 10, 5 per cent. Germination epiga^ous, caulicle reddisli, 

 f^mooth. Gotyledoiis elliptical, about 7 mm. ])y lo mm., rather 

 flesihy, veins not jn'ominent. Plumule and stem above the coty- 



2»Bot. Zeit., in.-,'), p. 185. pi. .',. 



*'A contribution to our knowledge of seedl'ngs, J. 4 79. 



*^A contribution to our knowledge of seedlings, }, jip. 499-501. 



