RECEPTION OF FLOWER-SEEKING ANIMALS AT THE FLOWER. 221 



warmth by movements, as when the sun's rays reach them in the morning after the 

 night's rest. But when, subsequently, they have once closed it is impossible to 

 make them open again completely the same day, vary the illumination as you 

 will. Indeed, in the majority of these flowers the closing occurs not towards 

 sunset, but at high noon; thus the heads of Lampsana and Tragopogon shut before 

 the sun reaches the zenith, and several hours before the maximum temperature 

 is attained. Then, again, there are the Dame's Violet {Hesperis matronalis), and 

 many Caryophyllacete, which only begin to open their flowers as light and 

 temperature wane, and shut them again ere the sun has risen. To explain these 

 movements as being a direct consequence of illumination and warmth were as 

 futile as to exj)lain the sleep of man and other animals as the immediate 

 consequence of on-coming night. Undeniably there is an indirect connection with 

 the change from light to darkness, from warmth to cold, but conceivable only in 

 the same manner as assimilation, metabolism and growth, in plants and animals, 

 observe the periodicity of day and night. We may state it in this way: in 

 different organisms certain resultant effects of assimilation, metabolism and growth 

 become manifest at different times, the particular time depending on the advantages 

 accruing to the organism in its special circumstances. For Man the night is the 

 most advantageous time for sleep; for Owlet Moths and other Noctuse it is not. 

 For Lampsana communis it is of advantage in respect of its ultimate self-fertiliza- 

 tion (to be described hereafter) that its capitula should close before noon, for the 

 Dame's Violet and numerous Catchflies (Silene), that their flowers should open in 

 the evening to receive visits from Moths (cf. p. 154). 



These observations oflfer no complete or satisfactory explanation. It still 

 remains unsolved how, in so many plants, periodic movements not depending 

 directly upon change in the environment have become hereditary. For those who 

 are satisfied with a fine-sounding Greek or Latin word in place of an explanation, 

 it may be remarked that these movements of floral leaves just described have 

 been termed Autonomous movements. 



EECEPTION OF FLOWER-SEEKING ANIMALS AT THE ENTRANCE 



TO THE FLOWER 



In a volume written years ago (Plants and their Unhidden Guests) I divided 

 the animals which come as guests to partake of the pollen, honey, &c., of flowers 

 into the bidden and unbidden. The former greatly profit the plant by their visits, 

 and there exist a multiplicity of arrangements for attracting them; the latter are 

 unprofitable and, frequently, positively disadvantageous; when they come they must 

 be hindered and sent away. The methods of flowers for attracting bidden guests 

 have been already described, the reception of these and the unbidden ones at the 

 entrance to the flower must now be considered. 



And first let us see what are the arrangements which exist to enable the bidden 

 guests to obtain the food they desire without loss of time, exertion, and, most 



