Chapter 7 



THE OVULE 



The angiosperm ovule consists of a central body, enclosed more or 

 less completely by one or two integuments and supported on a basal 

 stalk, the funicle. The central body consists of a distal part, in which 

 sporogenous tissue is borne, the nucellus, and a basal part, where 

 funicle, integuments, and nucellus merge, the cJmluza. The funicle may 

 be long, slender, and curved, or short and stout; when absent, the 

 ovule is sessile. The long funicle may be adnate to the ovule body, 

 forming a ridge, the raphe. The integuments enclose the nucellus more 

 or less completely and are commonly adnate to it, through part or all 

 their extent. In some, chiefly more primitive, taxa they are free from 

 the nucellus. The opening in the integumental sheath, where the tip of 

 the nucellus is exposed, is the micropijle. Where the integuments do not 

 reach the apex of the nucellus or spread distally, the micropyle is broad 

 and shallow; where the integuments extend well beyond the nucellus or 

 are thick, the micropyle is a long, slender canal, often constricted, some- 

 times irregular. The scar on the seed where it was attached to the fu- 

 nicle or the carpel wall is tlie hilum; the term is also applied to the 

 swollen tip of the funicle. 



Though there are, doubtless, only two true integuments, three and 

 even four have been described for some taxa. Reduced ovules without 

 integuments have been called naked. Where there are two integuments, 

 the proximal, or outer, is usually the more massive and characteristically 

 extends beyond the distal or inner; where there is only one integument, 

 this is usually massive and is often thicker than the outer one is where 

 two are present. Ovules with a prominent inner integument, which 

 projects well beyond the outer (Fig. 98C), are occasional, as in the 

 Annonaceae, Trapaceae, Proteaceae, some of the Cactaceae. Three in- 

 teguments have been reported for several taxa, but the "third integu- 

 ment," in at least most of these taxa, is a modified part of one of the 

 two normal integuments, usually a fleshy structure or aril. The term 

 aril is applied rather loosely to fleshy parts of the ovule: to prolifera- 

 tions of the chalaza, the integuments, or parts of the integuments, that 

 more or less completely envelop the ovule proper, extending upward 

 from the base or downward from the integument tips (as shown by 

 ontogeny); to outgrowths of the chalazal region; to fleshy funicles, as 



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