18 
regions, in rather alkaline deserts and the Reventi-arrecti which 
nave considerable differentiation in the same regions but spread to 
the north farther east. This last group amplifies into the Uliginosi 
a cosmopolitan group of plains, prairies and open woods in temper- 
ate regions. . This division on growing in cold meadows and dry 
valleys passes into the Hypoglottides, and this again divides into the 
Chaetodontes under the altered climatic conditions of the Columbia 
drainage. But it should be noted that, all three groups grow in the 
same region in the west, but each under its own peculiar ecological 
conditions. Another offshoot of the Homalobi, close to the Flexuosi 
is the Atrati of the interior juniper mesas, which branches into the 
Strigulosi which belong mostly to the cool meadows and mesas and 
pine forests of Mexico. : 
The second main branch of the Homalobi is the Flexuosi which, 
in the colder regions of the north in sweet soil branches into the 
Argophylli, a group growing on dry benches and plains where there is 
some winter snow. It shows some differentiation into the Malaci 
which also are replaced by Sarcocarpi of cold plains, and the Mollis- 
simi which extend beyond the limits of snow on plains to central 
Mexico, but in relatively cool regions. The Argophylli have some 
species that have secured some alkali tolerance, such as the species 
of the Navajo Basin. In the alkaline deserts and in clayey regions 
where the soil is very poor the Flexuosi pass gradually into forms 
with conspicuously inflated pods with rather thick walls, and the 
Ocreati and Bisulcati without inflation but with much alteration of 
walls by corrugations and sulcation at sutures and intrusion of the 
dorsal suture. The Bisulcati branch into the Galegiformes, and these 
again early give off the Lonchocarpi. The Flexuosi pass into the 
Hamosi which branch into the Leptocarpi, and these into the Micran- 
thi, and the latter pass into the Didymocarpi the highest developed 
species. This whole line of the Flexuosi is for the most part a line of 
warm and variably desert regions. A very few species grow in mo- 
derately cool regions such as bisulcatus, Drummondii, and some Ha- 
mosi, but they are for the most part the result of long inhabitance of 
hot regions of the south and subject to the greatest influence of 
diverse ecological conditions. 
In the system which I have used it has been my object to get 
related species together as far as a linear arrangement could do it. 
and I have therefore inverted the order of relationship in parts of 
groups to bring this about. 
In order to facilitate understanding the genetic relationship I 
have appended a diagram of my view of the relationship of the groups. 
My diagram of and arrangement of species is based wholly 
on relationship as indicated by the species of today. Whether this 
is the actual line of descent is a different matter for no one knows 
whether there has been retrogradation nor how much. A study of the 
Asiatic species might throw some light on this matter but the geolo- 
gical history is so localized that little benefit is liable to accrue from 
this source. The differentiation of the genus except in rare cases 
has manifestly been due to glacial and post-glacial agencies and these 
factors are well worked out. 
GROUP DETAILS. 
1. Homalobi. It is a debatable matter as to which species is 
the most primitive, but from its resemblance to Hosackia and Lathy- 
rus I have assumed A. campestris to be the most primitive. But 
for systematic reasons I have placed first those species with the 
ventral suture the more arched and which belong in more humid re- 
gions and mostly at the north. 
A. Wingatensis and tenellus fall together, with short or no stipe 
and small flowers. It is here that the Debiles branch off. The sti- 
