of Colour and Form in Plants, 407 



Euphrasia officinalis. 



Corolla purple, generally. 

 Odd lobe has yellow spot. 



Digitalis purpurea. 



Has white on odd lobe. 



In some species of Schizanthus and Collinsia we find purple 

 the prevailing colour; the primary, yellow, appears in the odd 

 lobe. 



In some genera with irregularity of flower often less marked 

 than in the examples alluded to, it is worthy of notice that the 

 two divisions on each side of the odd lobe frequently partake of 

 its characters as regards colour, half of each resembling the odd 

 piece ; Viola, Gloxinia, Achimenes, Rhododendron, &c. are ex- 

 amples. In some Thalamiflorous Exogens with irregular flower, 

 as Pelargonium and Tropaolum, we find that the two upper pieces 

 are usually largest, and present also the greatest variety in depth 

 of colour. In the Horse-chestnut there is a very decided relation 

 between the size of the petals and the intensity of the colour. 

 On each petal there is usually a crimson spot at the junction of 

 the limb and claw ; the size of this spot and its intensity are in 

 direct relation to the size of each petal ; the two upper being 

 largest, the two lateral smaller, and the odd. piece least of all. 



It may therefore be stated, that in some Thalamiflorous Exogens 

 with irregular corolla, owing chiefly to difference in size of the 

 petals, the largest are most highly coloured. 



Law 3. Different forms of corolla in the same inflorescence often 

 present differences of colour, but all of the same form 

 agree also in colour. 



The Coinpositse are illustrations of this : when there are two 

 colours, the flowers of the centre have generally one colour of 

 uniform intensity; those of the circumference agree together 

 also. 



The common Daisy has all the tubular flowers of the centre 

 yellow, and all the ligulate flowers of the ray are white, varie- 

 gated with purple. A yellow centre with purple ray is a com- 

 mon association in compound flowers, for instance, in species of 

 Aster, Rudbeckia, &c. 



The same general laws prevail in Monocotyledons as in Dico- 

 tyledons. In the former the calyx and corolla generally resemble 

 each other in structure and shape, and in colour also ; hence an 

 idea entertained by some that the perianth is single, relative 

 position having been overlooked. In Dicotyledons we generally 

 find a greater contrast between calyx and corolla as regards 

 colour. 



