THE ANGIOSPERMAE 



1 169 



are four small scales, alternating with the stamens, which can only be 

 reduced petals, but they are seemingly interior to the stamen whorl. The 

 development of the flower in the Proteaceae shows that the stamens and 

 sepals spring from quite distinct rudiments but they are carried upwards 

 together by intercalary growth of the sectors of the torus beneath them, 

 which does not aiTect the rudimentary 

 petals. The apparently exterior posi- 

 tion of the stamens is therefore attri- 

 buted tc this enforced association with 

 the sepals in the course of development 

 and there is probably no departure 

 from the normal order of succession 

 and alternation. 



The normal order of development 

 in the androecium is generally con- 

 ceived as being centripetal, that is to 

 say that the outer stamens develop 

 first and the inner w horls, if any, suc- 

 cessively later. The idea that this is 

 the universal order probably arises 

 from the fact that it obtains in several 

 of the most fully investigated families 

 such as Ranunculaceae, Rosaceae, 

 Papaveraceae, Leguminosae, Myrtaceae 

 and Nymphaeaceae. Corner has show^n 

 however that in a number of families 

 the order is reversed and is centrifugal. 

 The families for which this has been proved are Paeoniaceae, Dilleniaceae, 

 Hypericaceae, Capparidaceae, Tiliaceae, ?^Ialvaceae, Theaceae, Aizoaceae 

 and Cactaceae. The position of Paeonia in this group is interesting. It stands 

 apart from the majority of the Ranunculaceae in so many characters that it is 

 now often put, as above, in a separate family. The stamen development con- 

 firms this separation and associates the genus more closely with Dillenia- 

 ceae, a family to which it shows affinity in other respects. 



There is a much more definite hiatus in development between the 

 stamens and the petals in flowers with centrifugal stamens than in other 

 cases. Centrifugally developing stamens show no arrangement in para- 

 stichies. They form irregular whorls on a peripherally expanding floral 

 disc with, frequently, a doubling of the number of stamens in each whorl 

 outwards. Such stamens are often grouped in fascicles, a matter we shall 

 return to later. 



The adhesion of stamens to petals, especially in sympetalous flowers, is 

 of common occurrence and is known as epipetaly. If the sepals are involved 

 it is called episepaly (cf. Proteaceae, above). The degree of union varies 

 between a mere junction at the base, to a complete union of everything 

 except the anther and in a few rare cases, such as Viscum (Mistletoe) 



B 



Fig. 1 1 37. — Banksia sp. Proteaceae. A, 

 Flower. B, Flower cut vertically, 

 showing the small petal scales at the 

 base, in black. C, Upper part of sepal 

 with attached stamen. {After Le 

 Alaoiit and Decoisne.) 



