OVULE. [ 5' 



termed the funiculus (figs. 543 F, 647/) ; 

 the point of attachment of this stalk to the 

 body of the ovule (marked by a scar when 

 the ripe seed separates) is called the hilum. 

 That region of the interior where the lower 

 parts of the coat are confluent with the 

 base of the nucleus, is called the chalaza 

 (fig. 546 C). 



The form of ovules is much anected by 

 excessive development of their constituent 

 parts in special directions before the fertili- 



Fig. 546. 



Section of campylotropous ovule of the wallflower. 



C, chalaza; N, nucleus; Dinner coat; P, outer coat. 



Magnified 20 diameters. 



zation. If all parts grow equally, the com- 

 plete ovule is erect on the placenta, with its 

 hilum and also the chalaza turned towards 

 the latter, and its micropyle at the opposite 

 free end : such an ovule is technically termed 

 atropous or orthotropous (figs. 541-545). 

 Very frequently an excessive growth takes 

 place at one side of the coats of the ovule, 

 so that the chalaza is carried up and di- 

 rected away from the placenta, the micro- 

 pyle being at the same time turned down 

 towards the latter ; but as the growth is in 

 the coats of the ovule, the hilum remains at 

 the base, near where the micropyle arrives ; 

 such an ovule is termed anatropous (fig. 116, 

 p. 157). The hilum is then connected with 

 the chalaza by a ridge (a kind of adherent 

 funiculus) called the raphe. In other cases 

 the form becomes altered by the point of 

 the ovule turning down, the entire structure 

 becoming folded or bent upon itself, with- 

 out disturbance of the relative positions of 

 the hilum and chalaza, while the micropyle 

 is brought down, as in the anatropous 

 ovule, to the vicinity of the hilum. This 

 form is termed campylotropous (fig. 546). 

 Other conditions occur less frequently, 

 among which is the amphitropous form 

 (figs. 550 & 551). 



During these developments the embryo- 

 sac also undergoes various changes. Some- 

 times, as in the OrchidacesB, it expands so 



] OVULE. 



as to obliterate all the tissue of the nucleus, 

 and appears like a simple sac enclosed by 



Fig. 548. 



Fig. 549. 



Magnified 40 diameters. 



Fig. 550. Fig. 551. 



Magnified 20 diameters. 



Amphitropous ovule of mallow in different stages. 

 Fig. 551. Section. 



the coats; in the Scrophulariaceae and other 

 orders it produces peculiar lobes or pouches 

 at various points ; in the Santalacese it grows 

 out from the summit of the nucleus as a 

 free, naked, tubular process, &c. 



Up to this point the differences in ovules 

 are such as may be termed secondary ; but 

 a primary distinction now comes into view, 

 connected also with a difference in the ex- 

 ternal conditions, affording grounds for the 

 division of the Flowering Plants into two 

 great classes. In the Coniferse and Cyca- 

 dacese the ovules are developed upon open 

 carpels, and consequently the micropyle 

 may receive the pollen-grains immediately, 

 when expelled from the anthers. Plants 

 exhibiting this condition are termed GYM- 

 NOSPEBMS, or naked-seeded. In the Dico- 

 tyledons and Monocotyledons the carpels 

 are always closed up into cases or ovaries, 

 surmounted by a stigma, sessile or elevated 



