686 RYDBERG: PHYTOGEOGRAPHICAL NOTES 
ALPINE VEGETATION 
After having discussed the causes of the timber line, it is easier 
to define what an alpine plant is. In short, it is a plant that can 
endure the climate of the mountains above the timber line. It is 
a plant that requires less heat during the growing season than the 
forest trees, or that can survive a shorter growing season, or is 
less affected by frost, and besides can better withstand desiccating 
winds, deep snow, reduced precipitation, etc., or a combination of 
such conditions. Some authors claim that alpine and arctic 
plants are xerophytes, but they are not necessarily so. While 
most of the plants of alpine and arctic regions can withstand a great 
deal of drought, in fact are xerophytic plants, it is not the case with 
all. Not a few of the arctic-alpine plants require a great deal of 
moisture, growing only below and around snowbanks, or in springy 
or boggy ground, as for instance several species of Ranunculus, 
Saxifraga (in extended sense), Salix, and many grasses and sedges. 
There are in the arctic-alpine regions even true aquatics, as for 
instance among the phanerogams, Catabrosa aquatica, Phippsia 
algida, Sparganium minimum, and S. hyperboreum, and a few species 
of Potamogeton. 
NEw YorxkK BOTANICAL GARDEN 
