12 ELEMENTS OP STRUCTDBAL BOTANY. 



of honey, visit blossom after blossom, and, bringing theit 

 hairy limbs and bodies into contact with the open cells 

 of the anthers, detach and carry away quantities of 

 pollen, some of which is sure to be rubbed off upon the 

 stigmas of other flowers of the same kind, subsequently 

 visited. 



16. The essential part of the stamen is the anther, 

 and the purpose of this organ is to produce the -pollen, 

 which, as you have already learned, consists of njinute 

 grains, having a definite structure. These little grains 

 are usually alike in plants of the same kind. They are 

 furnished with two coats the inner one extremely thin, 

 and the outer one mucl. thicker by comparison. The 

 interior of the pollen-grain is filled with liquid matter. 

 When a pollen-grain falls upon the moist stigma it begins 

 to grow in a curious manner (Fig. 17). The inner coat 

 pushes its way through the outer one, ^ at some 

 weak point in the latter, thus forming the beginning 

 of a slender tube. This slowly penetrates the stigma, 

 and then extends itself downwards through the 

 Fig. 17- style, until it comes to the cavity of the ovary. 

 The liquid contents of the pollen-grain are carried down 

 through this tube, which remains closed at its lower end, 

 and the body of the grain on the stigma withers away. 



The ovary contains an ovule, which is attached by one 

 end to the wall of the ovary. The ovule con- 

 sists of a kernel, called the nucleus, which is 

 usually surrounded by two coats, through both 

 of which there is a minute opening to the nucleu?. -, 

 Tliis opening is called the rn^kropyle, and is. ^^ ^^ 



Fig. 17. — Pollen-grain developing a)-1itil>e.' 



Fig. 18 —Section of an ovule, showing central nucleus coats, and micropyle. 



