92 MORPHOLOGY OF THE ANCIOSPERMS 



be of individual organs or of entire whorls of organs; loss may be 

 minor, as loss of one petal or one stamen, or may occur in all parts of 

 the flower, so that there remain only the receptacle and one or few 

 sporophylls of one kind. All stages in loss of function and reduction in 

 size can be seen in closely related taxa. Organs in process of evolution- 

 ary reduction, "vestigial organs," can be recognized by abortive form 

 and structure and by position in the flower; vascular anatomy mav aid 

 in the interpretation of vestigial structures where identity is uncertain. 

 The vascular traces of lost organs are usually present when external 

 form is reduced, and may persist in the receptacle after the organ itself 

 has disappeared. 



Under reduction, organs may be reduced in form and structure and 

 changed in function. Transformations of petals and stamens into glands 

 and of stamens into staminodia are probably the commonest changes. 

 Evidence of the change of petals and stamens into glands is usually 

 apparent in position of the glands and type and origin of vascular sup- 

 ply. (Some glands and glandular surfaces represent merely secretory 

 areas, not modified organs.) Plants with nonfunctioning petals are 

 sometimes called apetalous when the petals are still present in vestigial 

 or greatly reduced form, as in the Proteaceae. In this family, some 

 genera have the petals present as laminar scales — Placospcrmum, 

 Austromuellej-a — or filamentous projections; others have glands in the 

 positions and with the anatomy of petals. In the Salicaceae, glands 

 that undoubtedly represent a lost perianth stand around, behind, or in 

 front of the sporophyll. The glands have the position and vascular 

 supply of perianth parts, and some of them are lobed and some- 

 what petaloid. The presence of a single gland seems to represent 

 the greatest reduction, because the willows, primitive in other floral 

 features, have several glands, and remnants of the vascular supply to 

 other lost perianth parts are found in species with a single gland. 



Reduction in the Stamen. Reduction in the stamen occurs in all stages, 

 from abortion of sporangia only, to complete disappearance of the or- 

 gan. The abortion of two sporangia — one of each pair — is frequent; 

 abortion of three of the four is rare. Loss of the entire anther is fre- 

 quent; the stamen survives as a sterile, laminar, or filamentous organ, 

 which may be petaloid. The petals of the majority of families seem to 

 represent completely petaloid stamens. Stages in the loss of the stamen 

 by gradual reduction in size of a staminodium are well shown in the 

 genera of the Scrophulariaceae. In genera where no external remnant 

 of the lost stamen survives, the vascular trace of the stamen is still 

 present in the receptacle. 



Reduction in the Carpel. Reduction in the carpel is primarily in size 

 and in number of ovules. Primitively, the carpel contained many ovules. 



