PAPERS ON BOTANY I 29 



the mat and tuft habits of many of its grasses. This is ac- 

 companied by a slow addition of humus to the soil, improving 

 its water-holding capacity, and this in turn reacting to cause 

 a closer stand of vegetation. This transformation seems grad- 

 ually to advance this succession to a more mesophytic associa- 

 tion differing from that described as the climax of the hy- 

 drarch succession principally in the smaller amount of such 

 species as Carex f estiva and other secondary species of rather 

 decidedly hydro-mesophytic character. Most of the grass 

 species of the dry grassland association are still to be found, 

 but the more xerophytic in decreasing abundance. The quan- 

 tity of Poa Muhlenbergia and Stipa has increased and such 

 forms as Deschampsia, Agropyron, Danthonia, Poa and Avena 

 have come in. The grasses now show a greater predominance 

 over other herbaceous plants although several new ones ap- 

 pear among the latter, the most conspicuous being Erigeron 

 macranthas that seems to be a rather constant indicator of 

 mesophytism. As previously noted this prairie-meadow asso- 

 ciation has a great variety of species, many showing peculiar 

 local abundance, but unfortunately neither the extent of our 

 investigations nor the space at our disposal permits their dis- 

 cussion in this paper. No more noticeable evidence of ad- 

 vancing mesophytism can be given than the data of Ramaley 

 that the bare ground in the prairie-meadow is not more than 

 10 per cent of the total area and that it is often entirely absent. 

 The question of the possibility of a forest invasion of these 

 grasslands seems quite as far from settlement as that of the 

 relationship of grassland and forests in Illinois and can not 

 be discussed at present further than to remark that while the 

 Colorado mountain grasslands show much evidence of great 

 permanency, indications are not lacking that they are areas 

 of potential forests and show the invasion of trees at certain 

 points. 



SUMMARY 



From the preceeding rather superficial observations the fol- 

 lowing agreements and differences may be noted as existing 

 between these Rocky Mountain grasslands and the prairies of 

 Illinois, as seen in the Chicago region : 



Agreements 



1. The two regions have very similar conditions of rain- 

 fall and humidity and in both there is a midsummer deficiency 

 in soil moisture. 



