1915] PLOWMAN—BOX ELDER 191 
elder; and to Professor Wir1tiAM TRELEASE for valuable sug- 
gestions and for his lively and encouraging interest in the progress 
of this work. 
WAUKESBA, WIS. 
EXPLANATION OF PLATES V-X 
Fic. 1.—Photograph showing the types of box elder leaves; +4. 
Fic. 2.—Trunk surface of box elder; X+. 
Fic. 3.—Trunk surface of Acer saccharinum; X%. 
Fic. 4.—Transverse section of the reuedaclive axis of Acer platanoides; 
X20 
Fic. 5.—Transverse section of the reproductive axis of box elder; X 20. 
Fic. 6.—Transverse section of young root of A. rubrum; X 20. 
Fic. 7.—Transverse section of young root of box elder; X 20. 
Fic. 8.—Transverse section of petiole of A. rubrum; X 20. 
Fic. 9.—Transverse section of petiole of box elder; X 20. 
Fic. 10.—Tranverse section of petiole of A. platanoides; X20 
Fic. 11.—Radial section of the bark and outer wood of an cides root of 
A. rubrum; X20 
IG. ia Prapeenes section of the bark and outer wood of an older root 
of A. rubrum; X20. 
1G. 13.—Transverse section of the wood and bark of a ro-year stem of 
box ca X 20. 
G. 14.—Transverse section of the wood and bark of a 12-year stem of 
es Htonites X20 
eS: si hewaaverts section of the wood and bark of an 8-year stem of 
A schon X20 
G. 16.—Transverse section of the wood and bark of a 20-year stem of 
A, Sone 20. 
Fic. 17.—Transverse section of a vigorous 1-year stem of A. saccharinum; 
AES. 
Fic. 18.—Transverse section of the midrib of the leaf of A. rubrum; X 25. 
Fic. 19.—Transverse section of a vigorous 1-year stem of box elder; X ro. 
Fic. 20.—Transverse section of a seed of A. platanoides; X8. 
Fic. 21.—Transverse section of a seed of box elder; X15. 
Fic. 22.—Tranverse section through the base of the samara of A. plata- 
noides; X8. 
Fic. 23.—Tangential section of the bark of A. rubrum; X 20. 
Fic 24.—Tangential section of the bark of box elder; X 20. 
Fic. 25.—Radial section of wood and bark of box elder; X 20. 
Fic. 26.—Radial section of wood of A. saccharinum; X 20. 
Fic. 27.—Transverse section of wood of A. saccharinum; X 20. 
