REPRODUCTION AND DISPERSAL 887 



they are of short duration; in most cases, however, as in the chickweed 

 (Stellaria media), the periods of vegetative and of reproductive activity 

 are coincident and of long duration; such plants may be called ever- 

 bloomers. As might be expected, everbloomers flourish particularly 

 in uniform tropical climates. While in temperate climates each month 

 or even each week from spring to autumn is characterized by the anthesis 

 of particular species, in uniform tropical climates almost any species 

 may bloom at almost any time, and a large number of species are true 

 everbloomers, being in flower at all times. Even those species which 

 are strictly periodic in temperate climates may be everbloomers in the 

 tropics (as in the grape and the Virginia creeper). In many species of 

 tropical everbloomers there is a suggestion of periodicity, since some 

 branches bloom at one time and some at another; for example, in the 

 grape one shoot on a given vine may be putting forth leaves and another 

 flowers, while still another is bearing ripe fruit. In such species the 

 phenomena exhibited by an individual branch are periodic, but taking 

 the plant as a whole the phenomena may be termed spasmodic. The 

 most representative everbloomers are plants with unbranched trunks, 

 such as Cocos or Carica, for in them there is essential continuity in both 

 vegetative and reproductive activity in a given shoot; new leaves are 

 found at all times, as well as flowers and fruits in all stages of develop- 

 ment. In many tropical plants, on the other hand, flowering is of rela- 

 tively rare occurrence, several years or even many years elapsing between 

 periods of anthesis. The most remarkable case of this sort is afforded 

 by a bamboo, Dendrocalamus stridus, which is said to flower regularly 

 at thirty-year intervals. Some tropical plants and even some plants 

 of high latitudes (as the duckweed) are almost never seen in blossom, 

 their reproduction being essentially vegetative. 



The relation of anthesis to meteorological factors. — While the occurrence 

 and the duration of flowering periods often have been regarded as due 

 to inherent causes, it always has been known in a general way that 

 climatic factors may hasten or retard such periods and modify their 

 length. If vernal plants bloom sooner than usual, the season is called 

 " early," while delayed anthesis causes a season to be called " late." 

 The observation of meteorological phenomena in connection with the 

 periodic activities of plants, and particularly of temperature in relation 

 to anthesis, is known as phenology. In a general way it is known that 

 temperature, among other factors, bears an important relation to flower- 

 ing, which is facilitated by high temperatures and retarded by low 



