30 THE STRUCTURE OF FLOWERS. 



Another correlation witli a quaternary arrangement is a 

 not nnfrequent valvate condition of the sepals at least, or of 

 the sepals and petals as well. These conditions prevail, for 

 example, in Oleacece, Onagracece, and, with the exceptional 

 genus, Clematis, of the Banunculacece. Too much stress 

 must not be placed upon this coincidence, as, if the petals 

 be enlarged through insect or other agency, the valvate 

 aestivation is often lost, and the petals become imbricate, as 

 in Fuchsia, Godetia, etc., though it is there retained in the 

 sepals. This valvate condition is foreshadowed in the ver- 

 nation of the foliage ; in that opposite leaves are almost 

 invariably valvate, having the two upper surfaces of the 

 leaves pressed together, as may be seen in Hypericum and 

 Vinca ; or else with the edges induplicate, as is characteristic 

 of Gaprifoliacece, resembling the sepals of Clematis.* 



Though the Onagracece have a preponderance of genera 

 with 4-merous flowers, there is in this order great variation 

 in the foliage. It is strictly opposite in Fuchsia and others, 

 but 14 genera out of a total of 22 have alternate leaves, while 

 with some, like Epilohium, it varies on the same stem. This, 

 I think, reveals the fact that the 4-merous condition has been 

 first established in the flowers, and subsequently the foliage 

 has varied from an opposite to an alternate condition in 

 certain genera, just as it does in an individual plant of 

 Fpilohiujii. 



That symmetrical reduction has elsewhere played an 

 important part in the origin of 4-merous flowers, is a sup- 

 position fully borne out by facts. In some cases it has 

 seemingly established itself as a permanent character, so that 

 systematists recognize it as generic or specific, accordingly, 



* See a paper by the author, On Vernation and the Methods of 

 Development of Foliage as protective against Radiation, Journ. Lin. Soc. 

 Bot., voL xxi., p. 624. 



