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A TEXTBOOK OF BOTANY 



[Ch. VI, 2 



I 



ovules in which the egg cells are fertilized by a method 

 to be fully described in the following section. 



The ovules are the most important parts of the pistils. 

 A typical ovule when mature shows the structure represented 

 by Figure 184. Innermost is the relatively large embryo 

 sac (large enough to be seen by the naked eye in sections 

 of very large ovules), containing much protoplasm which can 

 be recognized by its yellowish-brown color. In the sac lie 

 also several small cells (Fig. 190), amongst which is the one 

 of greatest importance, usually the 

 largest, the egg cell. This egg cell 

 when fertilized grows gradually to an 

 embryo plant within the embryo sac. 

 The embryo sac is imbedded within 

 a rounded mass of tissue called the 

 nucellus, which in turn is inclosed 

 by one or two integuments. These 

 grow up to surround the nucellus from 

 the stalk or funiculus, though they 

 never inclose the nucellus completely ; 

 for an opening called the micropyle 

 is always left for the entrance of the 

 pollen tube (Fig. 190). The funiculus 

 is sometimes straight, but oftener is 

 elongated and grown to the rest of the ovule, the resultant 

 ridge being called the raphe. In this way the ovule is swung 

 into positions facilitating the entrance of the pollen tube into 

 the micropyle (Fig. 185). . Through the funiculus runs a 

 vein which conveys food into the ovule as far as the meeting 

 place, called the chalaza, of nucellus, coats, and funiculus, 

 whence it passes by diffusion to the various parts. . 



Typically rounded in form, the ovary is often elongated, 

 cylindrically as in Peas, flattened as in Beans, or variously 

 angular. The style is almost wanting in the Peony, but in 

 some flowers is elongated even to thread-like, as conspicuously 

 in the silk of the Corn, while at times it is flat and quite petal- 



Fig. 187. — The Snap- 

 dragon, a typical irregular 

 (bilabiate) flower; X f. 

 (From Le Maout and 

 Decaisne.) 



