278 
IOWA ACADEMY OF SCIENCE Voi.. XXVIII, 1921 
Fig. 41. Ribes floridum. Wild black currant. Seedling showing cotyledons and 
early leaves. Glandular hairs, on leaves and petioles. Drawn by C. M. King. 
stem and petioles. These trichomes differ in length; they are 
slender, the cell at the top being enlarged. 
Rutaceae 
Ptelea trifoliata L. Hop tree. See figure 42. 
Seeds stratified out of doors ; planted in greenhouse March 25, 
1921. First germination appeared April 1, 1921, the seedling 
growing rapidly. Germination hypogaeous. The hypocotyl whit- 
ish, slightly hairy. Cotyledons fleshy, broadly elliptical, about 1/3 
of an inch in length, margin finely crenulate. 
First leaf shining, crenate-margined, smooth above, simple. 
The following leaf compound, three crenately margined leaflets ; 
third leaf the same. 
Aceraceae 
Acer saccharum Marsh. Sugar or Rock Maple. See figures 43, 
44, 45, 46. 
The seed was stratified out of doors in garden soil from Octo- 
ber 25, 1920, till April 15, 1921. When lifted several seeds were 
already germinating and all grew readily when transferred to the 
greenhouse bench. 
