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, calling 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; mstead 
of falling off speedily they become persistent when so 
affected. 
Some flowers are more lable to virescence than others. 
The common honeysuckle, Lonicera Periclymenum, 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 have the most folia- 
ceous portion of the flower remaining unchanged, 
while the corolla and other organs, usually less leaf- 
hike 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 
1 ‘De Antholys,’ p. 32, § 38. 
2 «Bull. Acad. Belg..’ xvii, part 2, p. 151, c. tab. 
