Formation and Succession Herbaria 5 



barium, as follows: (i) the gravel slide formation, (2) the half 

 gravel slide formation, (3) the pine formation, (4) the balsam- 

 spruce formation, (5) the spruce-pine formation. 



The value of formation herbaria in the exposition of a vege- 

 tative covering and the methods of arrangement and classification 

 to be employed are illustrated by the following descriptive list of 

 the Colorado formations : 



HERBARIA FORMATIONUM COLORADENSIUM 



PAGOPHYTIA: FOOTHILL FORMATIONS 



Bouteloua-Andropogon-psilium 

 The plains grass formation 



ASPECTUS AESTIVALIS 



Fades 



1. Bouteloua hirsuta Lag. 



2. Atheropogon curtipendulus (Michx.) Fourn. 



Species principales 



3. Talinum parviflorum Nutt. 

 3.1. Plantago purshii R. & S. 



4. Pentstemon unilateralis Rydb. 



5. Argemone intermedia Sweet 



6. Cleome serrulata Pursh 



7. Munroa squarrosa (Nutt.) Torr. 



8. Helianthus petiolaris Nutt. 



9. Verbena bracteosa Michx. 



Species secondariae 



10. Anogra pallida (Lindl.) Britt. 



11. Anogra coronopifolia (T. & G.) Britt.' 



12. Euphorbia cuphosperma (Engelm.) Boiss. 



13. Gilia aggregata (Pursh) Spreng. 



14. Asclepias pumila (Gray) Vail 



333 



