90 ^ The Plant Wori.d 



A few parasitic forms of the Perisporiaceae and other groups 

 occur from year to year on certain annuals, and a few sapro- 

 phytes have been found on bark, and, in two or three instances, 

 growing in the low ground of the wash. Undoubtedly careful 

 search would result in the collection of a considerable number 

 of species, but the fact remains that the fungus flora here is ex- 

 tremely limited, as it would seem it must be fro.n the severe con- 

 ditions imposed. This meager showing is again in contrast with 

 the rather rich display of fungi reported by Blumer in the Chiri- 

 cahuas, and probably matched in other neighboring mountain 

 regions where favorable conditions prevail. 



The symbiotic plants constituting the lichen flora have been 

 studied by Prof. Bruce Fink, to whose papers on this subject 

 reference should be made. 



(10) Cultivated Grounds, Waste Places, and Roadsides; 

 Miscellaneous Introduced Species. 

 Within the limits of Tumamoc Hill and the adjacent flood- 

 plain the introduction of weeds and of various cultivated species 

 has gone on until these have become, in many places, a conspic- 

 uous and more or less important element of the vegetation. 

 The high mallow {Malva parviflora) and cocklebur {Xanthium 

 canadense), for example, have greatly modified the aspect of 

 roadsides and edges of fields. Along the arroyos Arundinaria, 

 and near the old mill quince-bushes and Sapindus are permanent 

 reminders of the planting of earlier davs. Among later arrivals 

 are the afilaria {Erodium cicutarium) and foxtail (Hordeum 

 murimim), both of v/hich have made themselves at. home, and 

 their presence is materially felt over wide areas. 



The physiological requirements of these and numerous 

 other species introduced here, as well as their distribution in 

 relation to local conditions, are, to all appearances, much the 

 same as in the diff'erent regions froan which the\ came, but it is 

 noteworthy that they exhibit comparative indifl'erence to intense 

 insolation, much like indigenous species already referred to that 

 commonly grow in shady places. With one group as with the 

 other, a sufficient supply of soil-water is evidently the first es- 

 sential, and, with this assured, they flourish in the fierce glare of 

 the sun in an atmosphere often of very low relative humidity. 



