10 



Lakes. Four or five are fouud on the Great Plains east of the Rocky 

 Monntaius. In the Eocky Mountains proper there are twelve species, 

 of which three extend as far south as ^ew Mexico and Arizona. On 

 the Pacific slope from southern Alaska to California there are twenty- 

 five species in the mountains and along- the coast. On the Alaskan 

 peninsula and islands the genus is represented by seven species. 



Turning to the biologically more important distribution by life zones, 

 whose limits are fixed by sums total of effective temperature during a 

 definite period, we find the species pretty e(iually divided between the 

 Boreal and Transition zones— a distribution to be expected in a genus 

 of northern origin. Only a single species (C. imrpurascens) passes 

 timber line northward and on the higher Rockies, and becomes truly 

 Arctic- Alpine.' Several, notably C. breiceri in the Sierra Xevada, and 

 C. ne/jlectd, G. langsdorffii, and C. hyperhorca northward, extend into 

 the upper, or Hudsonian, belt of the boreal zone, in some cases probably 

 nearly reaching timber line. Other species, for example, C. cinnoidts 

 in the Atlantic States, and C. canadensis and C. hyperhorea elowjata in 

 the central prairie region, occur in country which is, broadly speaking, 

 upper Sonoran. It is probable, however, that the modifying infiuence 

 of a moist habitat accounts for such extensions, and that they are to 

 be regarded as outposts of the Transition. None of the species can be 

 regarded as of definitely Sonoran distribution. 



The following is an approximate classification of the species by 

 ioues. It must be noted, however, that the most careful and thorough 

 field work is necessary to make possible a complete and accurate defini- 

 tion of the zonal limits. 



1. Ap.ctic-Alpixe axd Boreal. — C. pnrpuiasctns. 



2. Boreal. — C. deschampsioides, lemmoni, breiveri, foUom{?), raseyi, tweedyi, aleulka, 



nihescens, breviseta, lan;jsdorffii, canadensis acuminata, scribneri, alaskana, laxijtoia, 

 netjlecta, micrantha, labradonca, hyperhorta, crassi(jhtmis, 



3. Boreal and Transition.— C. suksdorjii, canadensis, Injperborea elongata, hyper- 



bona americana. 



4. Transition. — C. bolanderi, hou-elJii, inontanensis, rilfaeformis, loehrioides, angusia, 



aiibjlvxuosa, fascicnlaia, suksdorjii iHsuriaw*, porU-ri, nemoralis, blanda {.') macouni- 

 ana, cuaickii, scopulorum, cinnoides, inexpansa, CaUfornica{f). 



ECOLOGY. 



Plants are classed in respect to habitat and the resulting adaptations 

 as hydrophytes (water plants), xerop^y^es (dry-soil plants), mesophytes 

 (intermediate as to moisture reijuireineut), and halophytes (salt-loving 

 plants), the last class, however, being of decidedly less importance than 

 the others. Nearly all the North American species of Calaniayrofitis- 

 belong to the first two classes, and the majority are hydrophytes. It is 

 noteworthy, however, that nearly all the species, even those growing in 

 the wettest soil, have characters that are generally supposed to belong 

 rather to xerophile i)lants, such as narrow, erect, strongly involute leaf 

 blades, short hairs or papilhc on the upper leaf surface, a thin coating 



