THE ESSENTIAL ORGANS THE PISTIL. 133 



The appearance of a free central placenta is presented in Caryophyllaceas 

 by the obliteration of the partitions which pass between the outer walls and 

 tne centre of the carpels. 



By Baillon a peculiar process from the placentas over the ovules is called 

 the obturator ; it is very conspicuous in Euphorbiacese. 



Various modes of Placentation. The placentas have been spoken 

 of as double, on account of their origin : where only one ovule 

 exists in a cell, it is assumed that one at least is suppressed ; but 

 this other is not unfrequently developed in the Cherry, Almond, 

 &c. (causing the double kernels). In Leguminosse the double pla- 

 cental base is so narrow that the ovules are placed one over another, 

 and form what appears like a single line. In Larkspur, Columbine, 

 &c. there is a distinct double row ; in many cases each placenta has 

 a double row of ovules ; while axile placentas are frequently thick- 

 ened and enlarged, so as to bear a large collection of ovules, closely 

 packed. In Papaver the ovules exist all over the imperfect septa ; 

 in Nymphcea all over the sides of the dissepiments, and not at the 

 margins ; in Butomus all over the inside of the carpels, &c. Where 

 ovules arise from the base of a carpel, either singly or in larger 

 numbers, the placentation is called basilar ; it is in most cases a 

 slight modification of free central. 



The Style. The styles require no particular notice beyond the 

 statements already made, except in regard to their irregular posi- 

 tion in some cases. The style is really produced from the apex of 

 the carpel ; but in various Rosaceae the ovarian part of the struc- 

 ture grows faster and so disproportionately that it leaves the style 

 on one side (lateral} (Frag aria, tig. 256), and sometimes even grows 

 out and up so much that the style, then called basilar, seems to 

 arise from the base (Alchemilla). In the Boragiuacese and Labiates 

 (fig. 205) a similar condition of the styles exists in a compound pistil ; 

 the styles in these plants are confluent, and arise as a solitary column 

 from a deep depression in the centre of the 4-lobed ovary, com- 

 municating with the cells near the base as in the Rosaceaa referred 

 to. These styles of Labiatae are called yynobasic. A dimorphic 

 condition of the pistil especially affecting the length of the style is 

 met with in some flowers, e. g. Primroses, some of which have short, 

 others long styles, as explained under Fertilization. 



The Stigma. The stigma is either situated at the end of the 

 style or, where this structure is wanting, it is sessile on the ovary. 

 Instances of sessile stigmas are furnished by the compound pistils 

 of Papaver (fig. 262), iNymphaeaceae, &c., where the stigmas form 

 radiating ridges on the top of the flattened ovaries. The elongated 

 stigmatic surfaces on the inner sides of the beak-like points of the 

 simple pistils of Hanuncuhis and allied plants are almost to be 



