POLLINATION BY BIRDS 93 



they are stored may be distributed through the tissues of all or certain 

 of the floral parts, or their presence may be restricted to the special 

 appendages described below. 



Nectar and Nectaries. — The nutritive substances other than pollen 

 to be consumed by the visiting insect, known as Nectars, are produced 

 by certain special glands and are stored in or upon contiguous receptacles 

 called Nectaries. The presence of these nectaries is commonly responsi- 

 ble for the outgrowth of the appendages to which they are often attached 

 (Figs. 63 and 65). At other times a part of the flower not conspicuously 

 modified produces and holds the nectar. 



Time of Activity. — The influences here described are in almost all 

 cases exerted at certain times which are especially favorable for securing 

 the desired results. In speaking of the perigone, it has been shown 

 that the duration of flowers varies greatly. It may be further stated 

 that those which perish quickly mature and expand at the particular 

 time of day when pollination is most likely to occur. Those which last 

 for several days enjoy a daily resting period and another period of 

 greatest activity, the details of which vary in different species or classes. 

 Commonly, the perigone becomes more or less folded or closed during 

 this resting period, its form and coloration legs conspicuous, the exhala- 

 tion of odors entirely suspended or greatly restricted, and access to the 

 nectar prevented altogether. At the same time that its functions are 

 thus inactive, its position is such as to afford it protection of various 

 kinds from dangers which are especially imminent during the hours in 

 which it rests. 



Sleep of the Flower. — This condition of inactivity or rest is commonly 

 spoken of as the sleep of the flower. It occurs at such a period of the 

 day as finds the agencies specially adapted to pollination in its case 

 themselves enjoying their rest. As these again become active, the 

 flower "awakens" and all the conditions above noted are reversed, or 

 at least such of them as affect the flower in question. 



Diurnal and Nocturnal Flowers. — Flowers in M'hich this active period 

 occurs during the day, whether they endure for but one day or longer, 

 are called Diurnal; those in which it occurs at night are called Nocturnal. 

 Besides the regular daily resting period, a great many flowers, by virtue 

 of special sensitiveness, possess the power of assuming such a condition 

 on special occasions when the conditions call for it. 



Pollination by Birds. — Humming-birds, as well as insects, are active 

 participators in the operations above recorded. Their operations 

 in promoting cross-pollination in the Cinchona group have been largely 



