456 



FOURTH GROUP. — SEED- PLANTS. 



very different families and orders which have usually less than five carpels, species 

 and genera with the typical five carpels do occur. 



The diagrams in Fig. 381-403 offer a selection of cases which, if no further 

 attention is paid to the consideration just mentioned, will come under the general 

 formula in its more simple expression SnPtiStn Cn{ — ;«). That the vacant places 

 marked with dots in the three outer whorls correspond to aborted members, in the 

 sense already frequently explained, can scarcely be doubted after comparison with 

 nearly allied forms, even in cases where those members are so absolutely wanting 

 that no traces are to be seen of them even in early stages of the development of the 

 flower ; this remark applies also where the carpels fall short of the typical number. 

 But there are other cases in which, as in J^/ius (Fig. 393), certain members, in the 

 case of J^^us two out of three carpels which show themselves, disappear in the course 

 of further development, two developing only as style or stigma, and one alone 

 is perfect. Crozophora tinctoria (Fig. 394) is particularly instructive on these 



points ; its flowers become unisexual because in the female flower the stamens 

 develope as sterile staminodes, the first step to abortion, while in the male flowers 

 the three carpels are replaced by three fertile stamens (Payer). 



In the introduction to the Angiosperms attention was called to the interposition 

 of a whorl of stamens between the members of an original whorl, and it was mentioned 

 that in obdiplostemonous flowers according to some observers the epipetalous 

 stamens are formed before the episepalous. Fig. 395 for example shows an 

 obdiplostemonous flower. The shaded stamens are the epipetalous ones, and they 

 stand further towards the outside than the episepalous ones. It is the same in most 

 Gruinales, among which however the Balsamineae have only the typical five stamens ; 

 but the Lineae and the genus Erodium show five more rudimentary stamens 

 interposed between these, while in Pegmtiwi Harmala and Monsonia the members of 

 the interposed and more exterior whorl are double in number. The arrangement in 

 the ^sculineae is of especial interest in this respect, because the interposed staminal 

 whorl remains incomplete in some of its families (Acerineae, Hippocastaneae, Fig. 396), 



