54 ORQANOGBAPHY. 



part, called the nucleus, surrounded by one or two integ- 

 uments (Fig. 130, ill). These integuments do not close 

 entirely above, but leave a small orifice, called the micro- 

 pyle (Fig. 130, mic). This is for the entrance of the 

 pollen-tube (Fig. 130, ^o^ tu), which grows from the pollen 

 grain that has been transported from the anther to the 

 stigma. 



68. In the upper part of the nucleus of the ovule is the 

 embryo-sac (Fig. 130, em. «), in which the embryo of the 

 seed is to be developed. This development, however, does 

 not take place till the ovules become fertilized, that is, 

 until the tube emitted by the pollen grain grows from the 

 stigma down through the style, enters the micropyle, and 

 reaches the embryo-sac, where the contents of the grain or 

 tube passes by osmosis into the embryo-sac. Unless, there- 

 fore, the pollen finds transport from the anther to the 

 stigma, there will be no production of seed. This transfer- 

 ence of the pollen is called pollination, and many contri- 

 vances and agencies exist to effect it, the most important of 

 which will now be mentioned. 



69. Pollination and Fertilization. — When both the 

 essential organs, stamens and pistils, are contained in one 

 and the same flower, as the Kose, Lily, Buttercup, Mint, 

 and Grass, it is called an hermaphrodite flower. Many 

 plants possess, either in the same cluster or on different 

 branchlets, both fertile (pistillate, that is, with pistils, but 

 no stamens) and sterile (staminate, that is, ^Yith stamens, 

 but no pistils) flowers, and they are said to be monoe- 

 cious (Gr. monos, one ; oihos, house), such as the Oaks, 

 Hickories, Alder, Corn, Nettle, etc. Others have the fertile 

 and sterile flowers on different trees, as the Willows, Pop- 

 lars, Ash, Hemp, etc., and they are called dicEcious (Gr. 



