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A TEXTBOOK OF THEORETICAL BOTANY 



Apart from the position of the ovule on the funicle is the question of its 

 position in relation to the ovary as a whole. The orthotropous ovule is 

 nearly always basal, with its micropyle upwards, but anatropous ovules 

 may occupy several alternative positions (Fig. 1293). If the raphe is on the 

 side towards the ventral suture of the carpel it is said to be ventral. The 

 ovule in this case faces outwards into the loculus. If the raphe is on the 

 other side of the ovule, namely dorsal, the ovule faces inwards towards the 



Fig. 1293. — Ovular positions. A, Ventral epitropous. 

 B, Ventral hypotropous. C, Ventral pleurotropous. 

 D, Dorsal pleurotropous. E, Dorsal epitropous. F, 

 Dorsal hypotropous. 



placenta. If the micropyle is upwards the ovule is epitropous, if downwards 

 it is hypotropous, and if directed horizontally it is pleurotropous. Basal 

 ovules may be either orthotropous or anatropous but pendulous ovules, 

 attached at the apex of the ovary, are invariably anatropous. In either case 

 the raphe may be ventral or dorsal. These differences may sometimes be 

 of systematic importance as family characters, but in a number of cases 

 differences of position may be seen within a single ovary. 



The order of development of ovules on the placenta follows one or other 

 of three possible directions, as is generally the case with serial developments, 

 i.e., basipetal, basifugal or in both directions from the middle. There is no 

 systematic significance in the direction. It is basipetal in Caryophyllaceae, 

 Solanaceae and Berberidaceae, basifugal in Cruciferae, Rutaceae and Lili- 

 aceae and mixed in Passifloraceae, Rubiaceae and Amaryllidaceae, to cite 

 only a few examples. Families are not always uniform in this matter and in 

 the Papaveraceae it varies between diflPerent genera. 



Certain features of structure in the basal, i.e., the chalazal portion of the 

 ovule require notice. Below the embryo sac, near the base of the nucellus, 

 there is often a group of cells with lignified or suberized walls, which Van 

 Tieghem called the hypostase. Although it is quite a prominent morpho- 

 logical feature in the ovules of some families, its function is doubtful. The 

 cells are not always thick-walled; sometimes they are richly protoplasmic 



