890 ECOLOGY 



solely in the wet period; the remaining 30 per cent are either everbloomers 

 or forms which overlap the two periods. 



In alpine and in arctic climates the flowering period is very short, often 

 not lasting more than two or three months. Plants that bloom in the 

 lowlands in April (as Erythronium and Claytonia) may not bloom until 

 June in alpine meadows, because of the long-continued cold and the 

 tardy melting of the snow at high altitudes. Strangely enough, however, 

 the alpine season soon catches up with that of the lowlands, so that by 

 July similar forms may be blooming at all altitudes, and in August the 

 alpine season actually is ahead of that of the lowlands; for example, 

 goldenrods and gentians commonly blossom sooner in the mountains 

 than at lower altitudes. Similarly, spring is much later and autumn 

 much earlier in high than in low latitudes; the farther grain grows from 

 the equator, the shorter is its maturation period, barley, for example, 

 ripening in ninety days in northern Norway, but requiring one hu idred 

 days in southern Sweden. In part this surprising phenomenon may be 

 due to the fact that alpine and arctic species are different from the low- 

 land species, and therefore, perhaps, inherently characterized by shorter 

 periods. That this is a minor matter in the explanation, however, is 

 shown by the fact that some of the species are common to high and to 

 low altitudes (as the yarrow and the harebell), but particularly by the 

 fact that alpine plants grown in the lowlands, or lowland plants grown 

 in alpine districts, behave in each case precisely like the indigenous 

 plants. Obviously, also, the usual phenological assumption that low 

 temperatures retard anthesis is the very reverse of the fact, for the heat 

 sums are much greater in low than in high altitudes and latitudes. 



It has been suggested that the greater intensity of alpine light and the 

 greater duration of arctic light, respectively, account for the "hurrying 

 up " of the seasons at high altitudes and high latitudes, enabling slants 

 to make the food necessary for anthesis in a shorter time. The experi- 

 ments about to be cited give another suggestion, namely, that those fac- 

 tors that are detrimental to vegetative activity and which, therefore, 

 cause its early cessation, are at the same time favorable to reproductive 

 activity. Among the factors in alpine habitats that tend to check op- 

 timum vegetative activity are low nocturnal temperatures,* great tem- 

 perature differences between day and night, high transpiration in pro- 

 portion to absorption, and, perhaps, intense light. 



The experimental determination of vegetative and of reproductive 

 periods. Adequate experimental study has shown that the length of 



