THE PROMISE OF THE PLANT THAT IS TO BE 465 



FIG. 570. UNIOVULAR OVARIES. 



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

 Dvule (d); (J) stalk (funicle) of ovule; 



The first diagram shows the ovary in secti 



are six pollen grains ; (6) style ; (c c) ovary containing a single inverted 

 (a) aperture (micropvle) of ovule through which the pollen-tube enters. In the second diagram the letters a to g are : 

 above, (h) Antipodal cells; (k) central nucleus; (in) egg-cell (oosphere) from which, after fertilization, the embryo 

 plant is developed ; (nti) co-operating cells (synergida?) ; (p) pollen-tube entering the micropyle; (r) inner envelope 

 of ovule' (*) outer envelope of ovule. The space containing It, k, m, n is the embryo-sac; the pi 



it (.r) is the nucellus. 



rt surrounding 



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 (#), 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 campylotropow 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 

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

 excellent example of this form. 



TI 12 



