336 



BOTANICAL GAZETTE 



[NOVEMBER 



canon is causing the invasion of this formation by various weed s 

 the commonest of which is Trijolimn repens. 



Common species of the middle layer are Geranium Richardsoniy 

 Rudbeckia anipla^ Aconittim cohimhianum^ Aquilegia coeridea, Viola 

 canadensis, Heracleum lanatiim^ and Vagnera stellala. Occasionally 

 a Mertensia ciliata from the brookside formation of the Hudsonian 

 zone wanders down the canons to 2250^. 



main 



Niittallii 



tenuifolia, with an occasional invasion of Pseudotsiiga mucronatay 



Popiilus 



In 



und is usually very 



middle la vers, in addition to the forms alreadv enumerated 



triangularis, Trollius albifl^ 



Thalicinim 



Oxypoli 



Montia 



Car ex canescens, Agrostis 



hiemalisy and Geum oregonense 



The 



middle layer here is usually open, but occasionally the grasses or 

 Carices form closed societies. 



F 



The formation is in a static condition. Within the canons at 

 least there is no aDDarent mierration of the cottonwoods takine: place, 



o 



Nuttallii has invaded the mountain 



to a point outside the proper limits of the formation. 



The observations made in a thicket of Corylus rostrata and those 

 in a hawthorn society, and recorded under the Populus occidentahs 

 formation, apply equally well to this formation, since these forma- 

 tions overlap at this point, as I have already mentioned. In addi- 

 tion ot these observations, I have three observations taken during 

 the summer of 1907. These observations were made at three stations 

 which I shall call A, B, and C respectively. Stations A and B w^ere 

 in Boulder Canon about 20^^ w^est of Boulder at an altitude of 

 about 2250^, while station C was at the mouth of Boulder Canon. 

 Station A was 6"^, B 6*^"^, and C 1.2^ from the edge of the stream. 



^ly observations follow: 



Station A, (June 26, 5 p.m.) 

 Station C, (July 30, 5 p.m.) 



Temperatures 









11° 



-15cm 

 i6?5 







14° 



I9?2 



pdm 



2I?2 



