Ig2 BOTANICAL GAZETTE [SEPTEMBER 
The mesa road was originally of the type just mentioned. During 
wet weather the road would be cut up to a certain extent and drivers 
would then turn to one side in order to escape the rough road. The 
new path has always been formed on the southwest side. This road 
has been in constant use for several years with the result that plants 
have been destroyed continually on one side, and have invaded the 
old roadways from the other. These old roadways show a great 
many stages in succession. 
The road is left in a somewhat roughened condition and the 
most important species to enter is Stipa Vaseyi. It thrives best in 
newer situations and disappears gradually as on* passes back from 
the well-formed frontal zone. The stable condition which it brings 
about is not favorable for the growth of the seedlings and it dies out 
after ten to fifteen years. Aside from the entrance of the annual 
ruderals Boebera papposa, Amaranthus blitoides, and Verbena brac- 
teosa, it represents the first stage in the succession which will result 
ultimately in the Bouteloua oligostachya formation. 
The species which ultimately take possession are usually deter- 
mined by the adjacent formation. Where Muhlenbergia gracillima 
is dominant it usually appears much in advance of Bouteloua 
oligostachya; but where the latter is dominant, it is usually in advance. 
Stipa Vaseyi, the first perennial to appear, is usually accompanied 
by the annuals Boebera papposa, Salvia lanceolata, P olygonum 
aviculare, Amaranthus blitoides, and a number of other species. 
The grasses enter in about the following order: Schedonnardus 
paniculatus followed by Sitanion elymoides and Aristida longiseld, 
and ultimately by Muhlenbergia gracillima and Bouteloua oligostachy4. 
With these grasses there appear many annual ruderals and also io 
following: Senecio s partioides, Gutierrezia Sarothrae, Artemisia frigid, 
Carduus undulatus, C. plattensis, and Pentstemon angustifolius. 
A transect of the mesa road will give more detailed information 
regarding the sucessions found here (see transect). This transect 1S 
one meter wide. In the plot each division represents one meter, 22 
the most important species in each square meter is placed at the left, 
and the other species in order of their importance are added to the 
right. 
