214 



JIANUAL OP BOTANY 



at the other parts of the ovule they are more or less distinct. 

 This chalaza is the point where the vessels pass from the pla- 

 centa, or vphen the ovule is stalked, from the funicnlws, into the 

 ovule, for the purpose of affording nourishment to it ; it is 

 generally indicated bj being coloured, and of a denser texture 

 than the tissue by which it is surrounded. Through the micro - 

 pyle the pollen-tube usually reaches the megaspore, as will be 

 hereafter fuUy described. 



Eelation of the Hilum, Chalaza, and Miceopyle to one 

 ANOTHER. — When an ovule is first developed, the point of union 

 of its coats and nucellus, called the chalaza, is at the base or 

 hilum, close to the placenta or fimieulus ; in which case a 

 straight line would pass from the micropyle through the axis of 



Fig. 470. 



Fig. 471. 



/'/;/. 469. Section of an ovule (diagramiufttie). tt. Nucellus. 6. Embryo- 

 sac, c. luuer coat, th Outer coat. c. Micropyle. /. Chalaza. g. Funi- 

 culus or fuuicle. Fi(j. 470. Verticil section of the orthotropous ovule 



of PoJtjgonum. c7i. Chalaza. pHni. Prlmine. spr. Secundiue. «. Nu- 

 cellus. -5. Embryo-sac. m. Micropyle. Flij. 471. A'ei-tical section 



of a campylotropous ovule of Wallflower (Ch^irant/ut.^). f. Fuaiculus. 

 eh. Chalaza. it. Primine. s. Secundine. n. Nucellus. mic. Micropyle. 



the nucellus and its coats to the hilum. In rare instances this 

 relation of parts is preserved throughout its development, as 

 in the Polygonacese {fig. 470) ; when the ovule is termed ortho- 

 tropous, atropous, or straight. In such an ovule, therefore, the 

 micropyle, m, is situated at its geometrical apex, or at the end 

 farthest removed from the hilum ; while the chalaza, ch, is placed 

 at its base. 



It sometimes happens, however, that the nucellus of the ovule, 

 instead of being straight as in the above instance, becomes more 

 or less curved. Thus in the Wallflower (fig. 471), and other 

 plants of the order to which it belongs, as well as in the Caryo- 

 phyllacese and many other plants, the apex of the oxule becomes 

 gradually turned downwards towards its base, and is ultimately 



