346 



PLANT MORPHOLOGY 



always becomes dry and woody at maturity but, in some genera, as in 

 Jumpcrus, the ripe cone is berry-like. In the Abietaceae each cone scale 

 bears two basal ovules on the adaxial side (Fig. 295D), but in the other 

 families the number is variable, being two to seven in the Taxodiaceae, 

 one to many in the Cupressaceae, and only one in the Araucariaceae. 



The ovules are inverted in the Ab- 

 ietaceae, Araucariaceae, and almost 

 all the Podocarpaceae; they are 

 erect in the Cupressaceae, Tax- 

 aceae, and almost all the Tax- 

 odiaceae. 



The ovule has a single integu- 

 ment (Fig. 297A). In the Abieta- 

 ceae the integument is fused to the 

 nucellus below but is free at the 

 apex, while in the other families, 

 with few exceptions, the integu- 

 ment and nucellus are either en- 

 tirely free or slightly united below. 

 The ovule of the Coniferales does 

 not develop a nucellar beak and 

 pollen chamber, their absence being 

 related to the fact that swimming 

 sperms are not produced. The in- 

 tegument consists of an outer fleshy 

 layer, a middle stony layer, and an 

 inner fleshy layer. The outer layer 

 is thin and usually disappears as 

 the seed ripens. Both inner and 

 outer sets of vascular strands have 

 been eliminated. The megaspore 

 mother cell is solitary and deep- 

 seated (Fig. 296B). It forms a 

 linear tetrad. As in other gym- 



B 



Fig. 296. Pinus nigra. A, longitudinal 

 section of young ovule, showing integument 

 (i), ovuliferous scale (s), bract (6), and 

 megaspore mother cell (m), deeply embedded 

 in the nucellus, X25; B, megaspore mother 

 cell surrounded by nucellar tissue, its 

 nucleus in prophase of the first reduction 

 division, X400. 



nosperms, the innermost megaspore alone is functional. 



In the Podocarpaceae and Taxaceae an outer fleshy covering grows up 

 around the ovule, uniting with it in Podocarpus and Torreya, but remain- 

 ing separate in Taxus. This fleshy structure has been interpreted by 

 some botanists as a second integument, by others as the ovuliferous scale. 



Female Gametophyte. As in the Cycadales and Ginkgoales, the devel- 

 opment of the female gametophyte involves several stages, as follows: 

 (1) free-nuclear division accompanied by the formation of a large central 

 vacuole that results in parietal placing of the nuclei; (2) wall formation; 



