1240 A TEXTBOOK OF THEORETICAL BOTANY 



become stigmatic where they are nearest together, thus forming a double 

 stigmatic Hne above each placenta. 



Leaving now the style and stigma, we must refer to one or two special 

 features of the gynoecium as a whole. First, there is the question of reduc- 

 tion in the gynoecium. Reduction in the number of carpels, often associated 

 with reduction in the number of ovules, is, as we have seen, a general 

 tendency in floral evolution. Thus pentamerous flowers often have only 

 three or two carpels, or even one, with consequent disarrangement of the 

 usual alternation of parts in successive whorls. Reduced numbers may be 

 stable throughout large circles of affinity. The dimerous gynoecium, for 

 example, is characteristic of most of the more highly evolved families of 

 Dicotyledons. Reduction may, however, occur as an exception. Thus, in 

 Cucurbitaceae, which have normally a trimerous gynoecium, reduction to 

 two or to one carpel may appear only in certain genera, by the suppres- 

 sion of one or two of the carpel rudiments. 



In Compositae the double stigma raises a suspicion that two carpels are 

 concerned in forming the single ovary and Small has recorded cases in which 

 two ovules were formed, either with or without a septum between them. 

 The Gramineae likewise have generally only a single ovule, although the 

 double stigma and the structure of the ovary wall indicate the presence of 

 two carpels. A very much reduced third carpel may, however, sometimes 

 take part in forming the ovary wall and in the Bamboos and in a few other 

 genera it is comparatively well-developed and bears a third stigma. Reduc- 

 tion to a single carpel does occur, though rarely, an example being Nardus. 

 The conclusion is that the typical Grass ovary has been reduced from the 

 trimerous condition which is general among Monocotyledons. 



In Cucos nucifera the familiar three depressions at one end of the woody 

 endocarp apparently represent a vestige of the three-carpellate condition. 

 Two of the depressions are woody and non-functional, but the third is soft 

 and provides a means of exit for the single seedling, through the hard 

 endocarp. 



In the above examples only traces, at the most, of the lost carpels are 

 retained, but there are numerous cases of carpels which fail, more or less 

 completely, to develop, although their rudiments are present in early 

 stages, occupying their appropriate places according to the symmetry of the 

 flower. Thus in Triglochin pahistre, three of the six carpels are solid and 

 sterile, though they continue to grow until the fruiting stage. In T. laxi- 

 florum all six carpels are alike and fertile. In Fedia, in Valerianella and in 

 Pontederia, two sterile carpels are found, which, although they retain a small 

 loculus, produce no ovules. In Viburnum only one sterile carpel occurs, 

 while in Valeriana and Centranthus only one carpel is formed and the two 

 sterile carpels have disappeared. All stages in suppression may, therefore, 

 be seen by comparison, from complete suppression of carpels to the 

 relatively minor degree of reduction in which one or more of the carpels, 

 although normally developed and producing ovules, are suppressed during 

 post-fertilization growth. The latter condition is exemplified by Aescidus 



