LESSON 18.] 



COMPOUND PISTILS. 



119 



are joined at the base only, or else below the middle (as in Fig. 

 254), and in some they are united quite to the top. 



312. Even when the styles are all consolidated into one, the stig- 

 mas are often separate, or enough so to show by the number of their 

 lobes how many simple pistils are combined to make the compound 

 one. In the common Lily, for instance, the three lobes of the stigma, 

 as well as the three grooves down the ovary, plainly tell us that the 

 pistil is made of three combined. But in the Day-Lily the three 

 lobes of the stigma are barely discernible by the naked eye, and in 

 the Spiderwort (Fig. 257) they are as perfectly united into 

 one as the ovaries .and styles are. Here the number of 

 cells in the ovary alone shows that the pistil is compound. 

 These are all cases of 



313. Compound Pistils with two or more Cells, namely, with 



as many cells as there are simple pistils, or carpels, that 

 have united to compose the organ. They are just what 

 would be formed if the simple pistils (two, three, or five 

 in a circle, as the case may be), like those of a Poeony or 

 Stonecrop, all pressed together in the centre of the flower, 

 were to cohere by their contiguous parts. 



314. As each simple ovary has its placenta, or seed- 

 bearing line (308), at the inner angle, so the resulting 

 compound ovary has as many axile placentae (that is, as 



many placentae in the axis or centre) as there are pistil-leaves in 

 its composition, but all more or less consolidated into one. This is 

 shown in the cross-sections, Fig. 254-256, &c. 



315. The partitions (or Dissepiments, as they are technically 

 named) of a compound ovary are accordingly part of the walls or 

 the sides of the carpels which compose it. Of course they are double, 



one layer belonging to each carpel ; and in ripe pods they often split 

 into the two layers. 



3 1C. We have described only one, though the commonest, kind of 

 compound pistil. There are besides 



317. One-Celled Compound Pistils, These are of two sorts, those with 

 axile, and those with parietal placentae. That is, first, where the 

 ovules or seeds are borne in the axis or centre of the ovary, and, 

 secondly, where they are borne on its walls. The first of these 

 cases, or that 



FIG. 257. Pistil of Spiderwort (Tradescantia) : the three-celled ovary cut across. 



