16 ON THE PROTRACEtE OF JUSSIEU. 



subsisting between this family and that of Thymeleae, 

 in which I believe the greater number of botanists will 

 allow that this envelope is really calyx : and as this latter 

 argument may be considered as the stronger, I shall endea- 

 vour to establish the identity of this organ in these two 

 families. In several of the Thymeleae, especially in Pimelea, 

 the loAver part of the tube of the calyx is, as it were, 

 jointed with the upper ; after the falling off of which, it 

 remains surrounding the fruit : this is also the case in 

 several genera of Proteaceae, as in Adenanthos of Labillar- 

 diere, in Isopogon, in Grevillea Clirysodendron, and still 

 more remarkably in Frank/andia, in which the persistent 

 tube becomes indurated and even nearly woody, a change 

 surely not likely to take place in a genuine corolla. But 

 though I have thus adopted the language of Jussieu, I am 

 decidedly of opinion that, in all families having a single 

 28] envelope, it will be still better to call it perianthium 

 or perigonium, which latter term was proposed by Ehrhart, 

 and is adopted by Decandolle. 



A circumstance meriting the attention of the theoretical 

 botanist, respecting the calyx in this order, is its invariable 

 division into four leaves or segments ; for the single excep- 

 tion noted by Linnaeus in his description of the male 

 flowers of Brabejum, he himself seems afterwards to have 

 distrusted, from the manner in which he has introduced it 

 into the amended generic character given in the Mantissa ; 

 and I may add, that in nearly 400 species of the order, 

 which I have examined, I have not met with a single 

 exception to this rule. 



With this uncommon constancy in point of number, it is 

 remarkable that there is, in the whole order, a strong ten- 

 dency to irregularity in form, the various kinds of which 

 are of great importance in characterising genera. 



Before the expansion of the calyx the margins of its seg- 

 ments are applied to each other; and from the unequal 

 degrees of cohesion in many cases subsisting among them 

 after expansion, several kinds of irregularity arise. I am 

 not sure that any term has been contrived for this manner 

 of aestivation, except it be the (estivatio valvata of Linnaeus ; 



