460 BOTANICAL GAZETTE [DECEMBER 
cavity in shaded and unshaded leaves of the same individual. Most of 
the species observed were growing in the Botanic Garden of Harvard 
University. No attempt was made to pick out particular families for 
examination, but notes were made on any leaves, especially of dicotyledo- 
nous trees or shrubs, that showed decided concavity of the upper surface. 
Some slight amount of deviation from flatness seemed almost universal. 
The observations were made on mature vigorous leaves during the first 
week in September. 
The leaves or leaflets examined in many instances showed a rather 
definite dihedral angle, as in a and 3, fig. z. More often the surfaces on 
each side of the midrib were decidedly curved, as in the cases c-f, while 
some leaves, as in g and h, showed no semblance of an angle in the cross- 
section, but formed a rather deep trough, with curved sides. 
Measurements of angles were made by means of two straight-edged 
pieces of brass, hinged at one end and applied outside the leaf or leaflet at 
right angles to the midrib. In case the leaf surfaces were somewhat convex 
beneath, the angle taken was that subtended by a tangent to the middle 
points of the halves of the leaf. 
Plants of 31 families of dicotyledons, comprising 52 genera and pos- 
sibly 200 species, were noted as showing decided concavity of the upper 
surfaces of the leaves. Little attempt was made to find out how generally 
marked leaf-concavity characterized the various species of the genera 
examined. In some instances, e. g., Viburnum, it occurred in almost all 
the species accessible for observation, while in other cases, e. g-; Magnolia, 
Acer, it was present in some species and absent in others. « e 
The following measurements of dihedral leaf angles or concavities 
were obtained: 
Species Angle in degrees, | Angle in degrees, shade 
Akebia quinata (leaflets).............. 106 167-180* 
Magnolia acuminata.........4........ 80-180 | 180 or recurved 
Astilbe decandra (leaflets)............. 80-153 180 or recurved (167) 
Hydrangea quercifolia................. 134-180 180 or less 
chizophragma hydrangeoides......... 28-1 180 or less 
Fothergilia Gardeni.. <5 2. 34 80-180 180 or less 
Robinia Pseudo-Acacia (leaflets)....... 90-137 180* 
Begonia semperflorens................ 23-50 108-180 
Aralia pentaphylla (leaflets)........... often semicircular 180 
Ligustrion Thota. occ. iene be 5 180 
Syringa vulgaris........... Sar SipaeeeA 55-145 130-180 
Cephalanthus occidentalis............. 102-153 180 
Viburnine mite. soso 83-105 180 
eee OLS 
* The chade] n Ve Nice ee a eee 1 by the foliage of the plant itself. 
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In the tu. Lod 1 Pipes oe ee | 1 
