888 ECOLOGY 



temperatures. Phenological observers, however, often have regarded 

 temperature as of such controlling importance that they have prepared 

 tables showing the total amount of heat necessary for flowering in the 

 various species. Such tables are almost worthless, since they fail to 

 include the many other factors involved, some of which, as soil moisture 

 or atmospheric moisture, equal or surpass temperature in importance. 

 Further, in preparing tables, temperatures below o C. commonly are 

 ignored, although they are certainly of considerable significance in some 

 plants (as in those of arctic regions), while the temperatures just above 

 o C. may be without significance in other plants (as in palms). 



The difficulties involved in discovering the factors that determine the 

 inception of anthesis are best illustrated in those species which form 

 flower buds early in the season previous to flowering. Some buds, as 

 in the lilac and the white birch, begin to develop a year before they come 

 into bloom, and in most vernal species the flower buds are in evidence by 

 midsummer. The insufficiency of the phenological method in the case 

 of such plants is most striking, since certain buds (as in the alder and 

 the hazel) that withstand days and even weeks of warm weather in the 

 autumn without blooming require but a few days of warm weather 

 in spring to induce anthesis. 1 Years ago it was shown that summer and 

 autumn temperatures have little or no influence upon the flower buds of 

 the cherry (Prunus Avium), though the buds are evident as early as 

 July; however, shoots taken into a hothouse in the middle of December 

 bloomed in twenty-seven days, whereas those taken in the middle of 

 January, in early March, and in early April, bloomed, respectively, in 

 eighteen days, in twelve days, and in five days. In some recent com- 

 prehensive experiments with nearly three hundred species of woody 

 plants, more than half of the twigs which were brought into a greenhouse 

 in November started to grow within two weeks; the twigs of seventy 

 species began to grow in February, and those of thirty-six species did 

 not become active until March. These results make it very obvious that 

 the influence of temperature or of other external factors upon anthesis 

 depends entirely upon the condition of the buds at the inception of the 

 experiment. While buds in February look much as they do in Decem- 

 ber, in reality they are different, one determinable change being that in 



1 Occasionally vernal species flower in autumn (as in the violet, strawberry, and apple), 

 particularly if favorable temperature and moisture conditions are long continued. The 

 wonder is that such phenomena are relatively rare, especially since some buds seem to 

 be fully formed by early autumn (as in the alder and the hazel). 



