GROUP V. ANGIOSPERM.E. 



469 



Fig. 284 <?), the placentation is termed free central. When there 

 is but a single ovule in the loculus, the placentation is basilar or 

 basal, and the ovule is erect : in this case the ovule is borne either 

 terminally at the apex of the floral axis (e.g. Polygonum, Piper, 

 Xaias, Tig. 284 F) ; or laterally, below or behind the actual apex 

 (e.g. Composites, Fig. 284 D). 



FIG. 231. Diagram* of the different mode* of Placentation. A Monomeroug ovary of 

 Helieborns, opened along the ventral suture ; t the ovules on (q) the marginal placenta. 

 B Transverse section of the ovary of Nicotiana : / wall of the ovary ; q placenta, largely 

 developed by the union of the margins of the carpels (axile placentation). C Transverse 

 section of the ovary of Bntomus. The ovules are scattered over the whole of the inner 

 surface, except the midrib, m (superficial placentation). D Longitudinal section of an 

 ovary of one of the Compositae : / the wall ; the erect, anatropous ovule () grows from the 

 base by the side of the apex of the axis, a. Longitudinal section of the ovary of one of 

 the Umbelliferae ; in each chamber an anatropous ovule is suspended. F Longitudinal 

 section of Bheutn ; a single erect orthotropous ovule grows at the apex of the floral axis. 

 G Longitudinal section of the ovary of one of the PrimulacesB; the ovules grow on a 

 prolongation of the axis (free central placentation). Fig. 282 B represents parietal 

 placentation. 



For other descriptive terms relating to the ovule, refer back to 

 p. 398. 



The macrosporangium, or ovule, consists primitively of a mass of 

 cellular tissue, the nucellus, invested by one or two integuments, 

 with a micropyle at the apex (see p. 398) : generally speaking, two 

 integuments are present in the Monocotyledons, in most polypetal- 

 ous Dicotyledons (with exceptions such as some Umbelliferse and 

 Ranunculacese), and in the Cucurbitacese among Gamopetalse ; 



