CHORISIS OK DEDUPUCATION. 207 



single in Senebiera and many species of Lepidium, in which the 

 lateral or short stamens are at the same time abortive. 



379. It is quite possible that chorisis may be extended to the 

 corolla of the cruciferous flower, and reduce the whole to a 

 symmetrical 2-merous plan, and to congruity in the perianth 

 also with Fumariaceae. The only obstacle is in the petals form- 

 ing a whorl of four where all the rest is 2-merous, for the sepals 

 are manifestly two decussating pairs. Now the median petals 

 of Hypecoum are deeply 3-lobed. An abortion of their middle 

 lobe would leave them almost two-parted : a little more would 

 separate them ; then they would imitate the four cruciferous petals 

 as in the diagram, Fig. 395. Applying this view to Cruciferae, 

 the blossom in the two orders would accord in having a 2-merous 

 three- whorled perianth, the first and third whorls median ; * as 

 also in the dimerous androecium, the first whorl of which is 

 lateral. The difference is that in Fumariacese the two members 

 of the first whorl of stamens augment by chorisis into three, and 

 the second is wanting, or is present only in Hypecoum ; while in 

 Cruciferae the first whorl is simple (of the two short stamens) , and 

 the second is doubled. In Fumariacese only the first whorl of the 

 perianth counts as calyx, and 



the corolla is of two whorls ; 

 in Cruciferae, the first and 

 second whorls are calyx, the 

 inner sepals answering to the 

 outer petals of Fumariaceae. 



380. Chorisis along with 

 anteposition of stamens is well 



seen in Tilia or Linden, at least in the American species. In 

 these the indefinitely numerous stamens are in five clusters, one 

 before each petal (Fig. 398, 399), and there is a petal-like body 



alternating with the calyx-members as a whole ; the short stamens following 

 as a 2-merous circle ; then the long stamens as a 4-merous circle ; lastly the 

 2-merous gyncecium. G. Henslow (in Trans. Linn. Soc. ser. 2, i. 195) would 

 have the flower 4-merous by the suppression of the fifth members of a 

 6-merous type, and a further suppression of half of the remaining exterior 

 stamen-circle, &c. Finally, there is the much better-maintained view that 

 the cruciferous flower is 2-merous throughout, as explained in the following 

 paragraph, 379. 



1 This view was taken by Steinheil, in Ann. Sci. Nat. ser. 2, 337 (1839), 

 and is essentially reproduced by a Russian botanist, Meschajeff, in Bull. 

 Soc. Imp. Nat. Mosc. 1872. 



FIG. 398. Diagram of the flower of Tilia Americana, the common American Lin- 

 den or Basswood. 



FIG. 399. A detached stamen-cluster with its petal-like scale. 



