198 Mr, B. Clarke on Relative Position; 



carpel posterior, and Lachnaa shows the sairie tendency in the 

 anterior stamens being longer. In Stilbe also the posterior sta- 

 men is rudimentary or absent, yet the larger cell of the ovary 

 which becomes the fertile is for the most part posterior, the an- 

 terior cell in S. ericoides being frequently obliterated. And 

 Pleurophora has the same structure when the posterior stamens 

 ai*e deficient. Possibly the truth may be, that when the single 

 carpel is anterior or lateral, the fertile stamens are also anterior, 

 rarely lateral ; but that when the position of the carpel is variable 

 there is no longer any constant relation between them, although 

 the posterior stamens continue to be far more frequently sup- 

 pressed. 



Characters therefore derived from the position of fertile sta- 

 mens are of less value than those derived from the position of 

 the single carpel, and the same remark may apply to the relative 

 position of floral envelopes, it being a question if Mimosese 

 always agree with Leguminosse in this character. The number 

 five however in Exogens may prove to be the consequence of the 

 non-development of a sepal or petal, as in the instance of the 

 calyx of a Phyllanthus consisting of six sepals becoming occa- 

 sionally reduced to five by the suppression of one of the external 

 three, and this would also account for the alternation of petals 

 and stamens in Exogens ; thus, supposing six stamens to be op- 

 posite six petals, and the anterior petal and the posterior stamen 

 to be removed, an ordinary pentamerous flower with the stamens 

 alternate to the petals would be produced. 



The Axis. 



In ascertaining the position of carpels, an uncertainty some- 

 times arises as to their position in consequence of a doubt existing 

 as to which is the axis, there being two or more branches, either 

 of which might be regarded as the axis to a flower growing in 

 connection with them ; but an attentive examination of the mode 

 of growth and of the position of the bracts, in specimens more 

 than usually developed, generally obviates this difficulty; it is 

 necessary however to observe, that in the construction of the 

 Tables, whenever any irregularity exists in the flower, that irre- 

 gularity is taken as a guide, as for example in Grevillea ; and 

 some allusions to modes of growth are subsequently added in 

 connection with the structure of ovaries. 



Conclusion. 



By arranging the Natural Orders in two divisions, it is not 

 intended so much to draw any exactly definite line by which to 

 separate them, as to show that there exists in Exogens two facies 



