THE FLORAL SHOOT. 421 



the tooth wort, trillium, lily, etc. The ovary is the enlarged part 

 which below is attached to the receptacle of the flower, and con- 

 tains within the ovules. The style, when present, is a slender 

 elongation of the upper end of the ovary. The stigma is sup- 

 ported on the end of the style when the latter is present. It is 

 often on a capitate enlargement of the style or extends down one 

 side, or when the style is absent it is usually seated directly on 

 the upper end of the ovary. The stigmatic surface is glutinous 

 or "sticky," and serves to hold the pollen-spores when they 

 come in contact with it. 



The ovules are within the ovary and are arranged in different 

 ways in different plants. The pollen-grain (or better pollen- 

 spore = micrpspo re), after it has been transferred to the stigma, 

 "germinates," and the pollen tube grows down through the 

 tissue of the stigma and style, or courses down the stylar canal 

 until it reaches the ovule. Here it usually enters the ovule 

 (macrosporangium) at the micropyle (in some of the ament- 

 bearing plants it enters at the chalaza), and the sperm-cells are 

 emptied into the embryo sac in the interior of the ovule. 



810. Fertilization. One of the sperms unites with the egg in 

 the embryo sac. This is fertilization, and from the fertilized 

 egg the young embryo is formed still within the ovule. Double 

 fertilization, the other sperm-cell sometimes unites with one 

 or both of the "polar" nuclei which have united to form the 

 "definitive" or "endosperm" nucleus. As a result of fertiliza- 

 tion, the embryo plant is formed within the ovule, the coats of 

 which enlarge by growth forming the seed coats, and altogether 

 forming the seed. (See Chapters XXXIV, XXXV, XXXVI.) 



II. Kinds of Flowers. 



811. Absence of certain flower parts. The complete flower 

 contains all the four series of parts. When any one of the series 

 of parts is lacking, the flower is said to be incomplete. Where only 

 one series of the floral envelopes is present the flowers are said to 

 be apetalous (the petals are absent), examples: elm, buckwheat, 



