274 BOTANICAL GAZETTE [OCTOBER 
GENERA WHICH CONTAIN THE MOST SPECIES. 
Genera Species | Genera Species 
WG es os eerecae es ba 52 “Trifo]fatias.e)ais acta ots 20 
Eriogonum........ 41 AU Iple Rs 6 os sies sraiel< 19 
Astragalus. ........ 35 Chorizanthe 22... 19 
PP DACEM A. isso ic ws 30 Millis.) oc. sacra 5 19 
Moan ced ers cares 30 FUNGUS): canis roses 18 
REPS ian tcc age 27 Pentstemon........ 18 
HOsackta so. 6 25 wees 22 OUTTA Mes a ien se oss 16 
Kirynitzkia.. << c6es 20 ASAIN cccals seid -0% 15 
The above sixteen genera contain 401 species, or 20 per cent. 
of all the species of the region. Except a single species of Tri- 
folium, they are all indigenous. It is worthy of notice that these 
most largely developed genera, with a few exceptions, are dis- 
tinctively western American. : 
| AFFINITIES OF THE FLORA. 
On a previous page I have attempted to indicate the more 
immediate sources from which our flora has been derived, but it 
may not be without interest to glance briefly at its relation to 
the wider problems of plant distribution. For this purpose the 
families may be divided into three groups: first, those of such 
equal development in the several zones as be accounted cos- 
-mopolitan; next, those having their greatest development in the 
temperate zone; and, lastly, those whose centers of development 
are in or near the tropics. 
Such an arrangement is shown in the table on the oppo- 
site page; Phytolaccaceae and Dipsaceae being omitted, since 
they are represented only by introduced species. The columns 
of percentage indicate the proportion of the number of families 
in each regional division to the whole number of families in each 
taxonomial group. 
It appears from this table that the families, leaving out of 
consideration the cosmopolitan ones, which, being of general 
distribution, have no present signification, are about equally 
divided between the tropical and the extra-tropical groups; 4 
result to be expected from the geographical and climatic position 
of the region. 
cee 
