Contributions to Western Botany, No. 10. 
BY MARCUS E. JONES. 
The following paper on Allium is the result of anattempt to 
arrange the species of onions in systematic order so far as they 
are known to exist in the Great Basin and adjoining regions. 
Outside species are mentioned by way of comparison, and all are 
arranged in what the writer believes to be the genetic order, so 
as to save repetition. Nearly all the Great Basin species have 
been studied critically in the field. The illustrations are all 
from actual bulb coats drawn to a scale of forty diameters, and 
each number under a figure represents the number of the species 
in this paper. 
. ZONAL DISTRIBUTION. 
Without going into discussion of the terms used in relation 
to zonal distribution, the writer will give a summary of what 
he published several years ago. The flora of the World is 
divisible into two grand divisions, Tropical and Temperate. 
Yhe Tropical flora is bounded by the isotherm of 58° annual 
temperature approximately but varies down to 56° in very dry 
regions, and above 60° in humid regions. For our region in the 
dry areas its characteristic zonal plant is Larrea tridentata, 
in California it is Adenostoma fasciculata. 
The Temperate grand division is separable into Lower, 
Middle, Upper, and Frigid. 
The Lower Temperate ranges down to 50-52° annual tem- 
perature according to the humidity, its characteristic zonal 
piant is Juniperus Utahensis (which gives the name Juniper Belt 
