330 



ORGAXOGRAPHT. 



Fig. 714. 



it is suspended. In other natural orders we find the position 

 var3dng in different genera, although generally constant in the 

 same ; thus in the Rosaceas, the genera Geum, Alchemilla, &c., 

 have an ascending ovule, while those of Poterium, Sanguisorba, 

 Sec, have it suspended, and in Potentilla, both ascending and 

 suspended ovules are found. In the Ranunculaceoe also, we 

 find the ovule varying in like manner as regards its position. 



We will now consider the position of the ovules when their 

 number is more than one. Thus when the ovary or loculus has 

 two ovules (Jbiovulate), these may be either placed side by side 

 at the same level, and have the same direction, as in Nuttalia, 

 when they are said to be collateral ; or they may be placed at 

 different heights, and then either follow the same direction, when 

 they are superposed, or one ovule may be ascending, and the 

 other suspended, as in JSsculus {fig. 714). The position of the 

 ovules also, in those cases where they are in de- 

 finite numbers, is usually constant and regular, 

 and similar terms are employed. When the num- 

 ber of ovules in the ovary or loculus is indefi- 

 nite, the relations are less constant, and depend 

 in a great measure upon the shape of the locu- 

 lus, and the size of the placentas. Thus in the 

 long ovaries of many of the Lcguminosa3 {.fig. 

 653) and Crucifcric {fig. 600), the oahiIcs are 

 superposed, and by not crowding each other 

 they will all be turned in the same direction; 

 Avliile, on the contrary, if the ovules are 

 numerous, and developed in a small space, 

 they will necessarily crowd each other, and 

 acquire irregular forms and varying posi- 

 tions according to the direction of the pres- 

 In describing these varying ])ositions 

 tlie same terms are used, as those referred to 

 when speaking of the relations of the solitary 

 These terms are also applied in the 

 same sense to the relations of tlie seed in the 



fore, iroin Jussieu. 



pericarp. 

 Formation and Structure of the Ovule. — The ovule 

 appears at first, as a little roundish cellular projection on the 

 placenta ; tliis gi'adually enlarges and acquires ultimately, a 

 more or less ovate or somewhat conical I'orm ; this body is 

 termed the nucleus {fig. 715). It is at first perfectly uniform 

 in texture and ai)])earance, ])resenting no cavity as distinct irom 

 those of the ordinary jjarenchymatous cells of which it is com- 

 posed, and having no integuments. As development proceeds 

 a cavity is formed at or near the apex of the nucleus {fig. 716), 

 in which the embryo or future plant is developed ; hence this is 

 called the cmhnjo-sac or sac of the amnios. In rare cases, as iu 



Fig. 714. a loculus 

 of the ovary of a 

 species of uEscu- 

 lus containing two g^-e 

 ovules, one of 

 which is ascending 

 and the otlier sus- 

 pended; m micro- 

 pyle. Tlie other OVUie 

 letterB refer as be 



