THE PKOMISE OF THE PLANT THAT IS TO BE 465 



FIG. 570. UNIOVULAR OVARIES. 



The first t.liau'm 



the ovary in section before fertilization (the ovule not in section), (a) Stigma, upon which 

 six pollen grains ; (b) style ; (c c) ovary containing a single inverted ovule (d) ; (/) stalk (funicle) of ovule ; 



(g) aperture (micropyle) of ovule throug 

 above, (h) Antipodal 



hich the pollen-tube enters. In the second diagram the letters a to g are as 

 ells ; (/) central nucleus ; (m) egg-cell (oosphere) from which, after fertilization, the embryo 



plant is developed ; (nn) co-operating cells (synergidse) ; (/>) pollen-tube entering the micropyle; (r) inner envelope 

 f ovule; (*) outer envelope of ovule. The space containing h, k, m, n is the embryo-sac; the part surrounding 



it (.r) is the nucellus. 



The second diagram shows the same pistil, but ,with the ovule also in 

 section. Observe the structure of the ovule, here represented at the stage 

 immediately preceding fertilization. Commencing from the outside, we 

 have first a coat or envelope (s) the outer integument ; secondly, an inner 

 coat (r) the inner integument ; and within that a mass of tissue (a;), repre- 

 sented by the dark shading the nucellus. Embedded in the nucellus is the 

 embryo sac, which contains an abundance of protoplasm, with large vacuoles 



or campylotropous form, in which the ovule curves upon itself like a horseshoe, and so 

 brings the micropyle near the base. This is well seen in the Pea (fig. 571) and in the 

 seeds of Shepherd's Purse (Capsella bursa-pastoris). Straight or orthotropous ovules, 

 which have the funicle and nucellus in the same straight line, are common among the 

 (Tymnosperms, and occur also in the Dock family. The Yew (Taxus baccata) offers an 

 excellent example of this form. 

 n12 



