CAMPANULACEOUS AND OLEAOEOUfl ORDERS. 3 



so definitely characterizad by the indusium as to have no ambi- 

 guity in its circumscription. The homology of this indusium has 

 been variously interpreted. R. Brown, in the then state of our 

 acquaintance with the organs of other plants that might be com- 

 pared with it, put the following queries (Trans. Linn. Soc. xii. 

 134) : — "Is this remarkable covering of the stigma merely a pro- 

 cess of the apex of the style ? or is it a part of distinct origin, 

 though intimately cohering with the pistillum ? On the latter 

 supposition, may it not be considered as analogous to the glan- 

 dular disk surrounding or covering the ovarium in other families ? 

 And in adopting the hypothesis I had formerly advanced (Trans. 

 Linn. Soc. x. 159) respecting the nature of this disk in certain 

 families, namely that it is composed of a series of modified sta- 

 mina, has not the part in question a considerable resemblance in 

 apparent origin and division to the stamina of the nearly related 

 family Stylidiaceae ? To render this supposition somewhat less 

 paradoxical, let the comparison be made, especially between the 

 indusium oiBrunonia and the imperfect antherae in the female 

 flowers of Forstera" All further observation, however, has 

 tended rather to oppose than to confirm this supposition. 

 Brown's idea of the conformity of the disk, scales, and stamens as 

 alluded to in the passage above quoted, appears to have been 

 founded, not so much on his own observation, as on Labillardiere's 

 having given the name of sterile stamens to the hypogynous 

 glands or scales of CenarrJienes, which glands, however, in fact 

 give no indication of any structural or morphological analogy to 

 stamens. It is very rarely indeed that the disk has been shown 

 to be a rudimentary whorl of organs, whether a reduced remnant 

 of extinct organs or a first development of new ones. It is, on 

 the contrary, now generally admitted that whether peripetalous, 

 as in the case of the ring of calycine glands or scales in many 

 Apocynese and Aselepiadeae, or peristaminal, as in some Polypeta- 

 lous orders or genera, or, as is more frequently the case, truly pe- 

 rigynous, hypogynous, or epigynous, the disk is a mere outgrowth 

 of the receptacle or summit of the floral pedicels, promoted pro- 

 bably in many instances by the attractions its secretions afford to 

 insects and then a true nectary, possibly developed in others as a 

 store of nutriment during the early stages of the young embryo, 

 but seldom, if ever, independently organic. If on some occasions 

 it shows a ring of lobes alternating with those of the androecium 

 or other immediately external whorl, that is merely due to the 



b2 



