330 



IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



mottled with red, are at first folded, expanding later, directed 

 obliquely upward, slightly curved toward the tip, fleshy, both 

 under and lower surface smooth, glaucous on the under surface. 

 The young leaves are lighter in color on the under surface, and 

 slightly hairy, but are not glaucous. 



Acer saccharwn var. nigrum (Michx. f.) Britton.. Black Sugar 

 Maple. Described May 6, 1917. Height two inches. Plants 

 germinating abundantly May 5, 1917. Germination epigaeous; 

 hypocotyl (caulicle) green, thickened, fleshy; root much smaller; 

 cotyledons thickened, fleshy, smooth, entire, sagittate at the 

 base; plumule slightly hairy. The first leaves palmately three 

 lobed, with the form characteristic of the adult, green on both 



Fig. 104 Fig. 105 



Fig. 104. — Germination of black maple (Acer nigrum). Fleshy elongated 

 cotyledons and the drooping leaves, coarsely toothed and rugose. Photo- 

 graphed by Photo. Section, F. E. Colbum. 



Fig. 105. — Germination of box elder (Acer negundo) , radicle caulicle, the 

 erect cotyledons and simple opposite leaves. Photographed by Photo. Section, 

 V. E. Colburn. 



surfaces. Trichomes simple, walls fairly thick, a few longitu- 

 dinal striae giving the wall a roughened appearance. Protoplas- 

 mic contents granular, nucleus small. Hair tapering but not 

 acutely pointed. Other slender trichomes present, unicellular, 

 long, twisted like cotton fibers. 



Acer negundo L. Box Elder. Germination epigjeous. Seeds 

 become stratified on the ground. Germination observed to begin 

 April 19, 1917, and continued to May 1, 1917, about 80 per 



