THE WEATHER. 227 



odicity of the annual phenomena of nature. It usually studies 

 climate and the progression of the seasons in terms of plant and 

 animal life, as the dates of migrations, of blooming, leafing, 

 ripening of fruit, defoliation, and the like. If observations are 

 to have permanent value, they must be taken with a definite 

 purpose. The particular objects of phenological observations 

 are the following : 



1. To determine the general oncoming of spring. 



2. To determine the fitful or variable features of spring. 



3. To determine the epoch of the full activity of the advanc- 

 ing season. 



4. To determine the active physiological epoch of the year. 



5. To determine the maturation of the season. 



6. To determine the oncoming of the decline of fall. 



7. To determine the approach of winter. 



8. To determine the features of the winter epoch. 



9. To determine the fleeting or fugitive epochs of the year. 



Good phenological observations upon plants should satisfy 

 the following tests, as given by Hoffmann : 



1. They should represent as broad a distribution as possible 

 of the given species, selected for observation. 



2. Ease and certainty of identifying the definite phases 

 which are to be observed. 



3. The utility of the observations as regards biological ques- 

 tions, such as the vegetative periods, time of ripening, etc. 



4. Representation of the entire vegetation period. 



5. Consideration of those species which are found in almost 

 all published observations, and especially of those whose devel- 

 opment is not influenced by momentary or accidental circum- 

 stances, as is the dandelion. 



The epochs of vegetation which should be observed for most 

 phenological purposes are these : 



1. Upper surface of the leaf first visible or spread open. 



2. First blossoms open. 



