98 THE BIOLOGY OF THE SEASONS 



While Mr. Clarke's thesis seems to have a considerable 

 body of evidence to support it, we cannot regard it as 

 more than a partial interpretation. The problem is a 

 complex one, and, as Mr. Clarke recognises, the time when 

 a flower blooms is a function of many determinants, both 

 fixed and variable. It may be of interest to tabulate these. 



(1) Much depends upon the plant's peculiarities of 

 constitution ; thus those that have stores of reserve 

 material, which means energy, in corm and bulb, tuber 

 and rhizome, stem and evergreen leaves, will be able to 

 flower earlier than those that have no reserves. 



(2) Of importance also is the nature of the plant's 

 habitat and its availability at different seasons. " The 

 Spring flowers seek largely the protection of the wood- 

 lands ; marsh plants reach perfection mainly in latest 

 Spring and through the Summer, though some, like Caltha, 

 are early ; the aquatics of ponds and river glory in the 

 Summer sun ; and the flowers of meadow and prairie and 

 thicket margin luxuriate from Midsummer to the end of 

 Autumn." 



(3) Another factor is the mode of pollination ; by wind 

 or by insects, and by some kinds of insects rather than 

 others. It is plain that we cannot look for a large pro- 

 portion of insect-pollinated flowers in very early Spring. 

 It is true that insects may, in the course of time, adapt their 

 life-history to suit the flowers on which they depend, but 

 it is obvious that a bee-pollinated flower is not likely to 

 survive if it takes to blossoming only at a time when there 

 are no bees about. 



(4) Something must also be allowed for the geographical 

 origin of any particular plant. A wanderer from a colder 

 country will naturally flower early in its new home. 



(5) After allowing for these (and probably other) 

 factors, we return to the thesis that the time of flowering 



