FERTILIZATION OR FECUNDATION. 235 



denominated the " poor man's weather-glass." The closing of many 

 flowers in such circumstances protects the pollen from the injurious 

 effects of moisture. 



485. The expansion and closing of flowers is regulated by light and 

 moisture, and also by a certain law of periodicity. A plant accustomed 

 to flower in day-light at a certain time, will continue to expand its 

 flowers at the wonted period, even when kept hi a dark room. De- 

 candolle made a series of experiments on the flowering of plants kept 

 in darkness, and in a cellar lighted by lamps. He found that the law 

 of periodicity continued to operate for a considerable time, and that 

 in artificial light some flowers opened, while others, such as species 

 of Convolvulus, still followed the clock hours in their opening and 

 closing. 



486. Light has been said also to have an effect on the direction which 

 flowers assume. Some Compositor, as Hypochasris radicata and Apar- 

 gia autumnalis, are stated by Henslow to have been seen in meadows, 

 where they abound, inclining their flowers towards the quarter of the 

 heavens in which the sun is shining. A similar statement has been 

 made regarding the Sun-flower, but it has not been confirmed in this 

 country at least. Perhaps in its native clime, where the effect of the 

 sun's rays is greater, the phenomenon alluded to may be observable. 

 Vaucher mentions the effects of light on the direction of the flowers of 

 many plants, as Narcissuses and certain species of Melampyrum. 



487. It is of importance, both as regards meteorology and botanical 

 geography, that observations should be made carefully on what are 

 called the annual and diurnal periods of plants : the former being the 

 space of time computed between two successive returns of the leaves, 

 the flowers, and the fruit; and the latter, the return of the hour of the 

 day at which certain species of flowers open. The same species should 

 be selected in different localities, and care should be taken that the 

 plants are such as have determinate periods of flowering. Rules as 

 to the mode of observing periodical phenomena in plants have been 

 drawn up by the British Association, and a committee has been ap- 

 pointed to carry this into effect. The committee has published (1.) a 

 list of plants to be observed for the periods of foliation and defolia- 

 tion ; (2.) a list of plants to be noticed for flowering and ripening of 

 the fruit; (3.) a list of plants to be observed at the vernal and autum- 

 nal equinoxes, and summer solstice, for the hours of opening and closing 

 then: flowers. 



5. FUNCTIONS OF THE STAMENS AND PISTIL FERTILIZATION OR FECUNDATION. 



488. The stamens and pistil are called the Essential Organs of 

 flowering plants, inasmuch as without them reproduction cannot be 

 effected. The stamens, considered as the male organs, prepare the 



