338 ALTERATIONS OF COLOUR. 



Virescence. Engelmann* pointed out that, so far as 

 flowers were concerned, there are two ways in which 

 they assume a green colour, either by a simple develop- 

 ment of chlorophyll in place of the colouring matter 

 proper to the flower, Or by an actual development of 

 leaf-like organs in the room of the petals frondes- 

 cence. Morren^ judiciously proposed to keep these two 

 conditions separate, calhng the one virescence, the 

 other frondescence (see p. 241). 



Many of the cases recorded as reversions of the 

 parts of the flower to leaves are simply instances of 

 virescence ; indeed, it is not in all cases easy to dis- 

 tinguish between the two states. The examination of 

 the arrangement of the veins is often of assistance in 

 determining this point ; for instance, if, under ordinary 

 circumstances, the venation of the petal be such as is 

 characteristic of the sheath of the leaf, while in the 

 green-coloured flower of the same species the venation 

 is more like that which belongs to the blade of the 

 leaf, the inference would, of course, be that the green 

 colour was due to frondescence or phyllody. 



The persistence or duration of petals is often in- 

 creased when they are subject to this change ; instead 

 of falling off" speedily they become persistent when so 

 affected. 



Some flowers are more liable to virescence than others. 

 The common honeysuckle, Lonicera Perkhjmenum, is 

 one of these, and it is noticeable in this plant that the 

 calyx remains unaffected a circumstance which Morren 

 says shows the distinctness of virescence from frondes- 

 cence ; for, in this instance, we Jiave the most folia- 

 ceous portion of the flower remaining unchanged, 

 while the corolla and other organs, usually less leaf- 

 like in their nature, assume a green colour ; but this 

 may rather be attributed to the axial nature of the 

 so-called adherent calyx. The stamens in these green- 

 flowered honeysuckles are usually green also, but with 



' Do Antholvs,' p. 32, 38. 



' Bull. Acad. Belg..' xvii. p.art 2. p. 131, c. Uib. 



