20 
EDMUND W. SINNOTT AND IRVING W. BAILEY 
the three originally distinct leaf bundles were pulled together into a 
single strand, the midrib. 
5. Among woody plants, the multilacunar (more ancient) nodal 
type predominates in temperate regions and the unilacunar (more 
recent) in the tropics. The palmate lobed leaf among such plants is 
also almost entirely confined to temperate regions. These facts, in 
company with others, indicate that the Angiosperms first appeared 
under a climate more temperate than tropical, a climate in the Meso- 
zoic probably found only in the uplands. It is suggested that the 
absence of the earliest Angiosperms as fossils may be due to their 
confinement to such upland regions, where preservation would be very 
difficult. 
6. Evidence from the leaf strongly favors the view that the Angio- 
sperms sprang from a coniferous (palmate) rather than from a cyca- 
dean (pinnate) stock. 
7. The Monocotyledons were derived from some ancient palmate 
group of Dicotyledons. 
The writers are much indebted to the authorities of the Gray 
Herbarium and of the Arnold Arboretum for the use of their libraries 
and herbaria. 
BussEY Institution, 
Harvard University. 
DESCRIPTION OF FIGURES OF PLATES I-IV 
Fig. I. Acer carpinifolium Sieb. & Zucc. (pinnate simple). 
Fig. 2. Acer tataricum L. (palmate simple). 
Fig. 3. Acer ginnale Maxim., vigorous leaf (palmate lobed). 
Figs. 4 and 5. Acer ginnale Maxim, leaves of less vigorous growth. 
Figs. 6 and 7. Acer glabrum Torn, two leaves from the same twig showing 
origin of palmately compound type. 
Figs. 8, 9, 10 and i i. Acer Negundo L., series of leaves showing transitions from 
trifoliate to ternately compound. 
Figs. 12 and 13. Rubus negroensis Elm. and Rubus benguitensis Elm,, tropical 
species reduced from primitive type. 
Fig. 14, Rubus odoratus L., presumably primitive type for the genus. 
Fig. 15, Rubus neglectus Peck, leaf showing the transition from palmately to 
pinnately compound. 
Figs. 16 and 17. Solanum nigrum L. and Solanum carolinense L. two closely 
related species showing transition from pinnate simple to pinnate lobed. 
Figs. 18 and 19. Ampelopsis tricuspidata Sieb. & Zucc, a leaf of vigorous and 
one of weaker growth. 
