The^e colours are found appropriated to different parts of the plant. For 

 instance, water-colour is found chiefly in the filaments of stamens and the styles 

 of pistils; white in the centres of the cups of crateriform, and malvaceous flowers, 

 which are less exposed to the light ; and in that part of the stem which is under- 

 ground. Yellow is found chiefly in the anthers and stigmas, but frequently in 

 the corolla. Blue and violet almost exclusively appear in the petals, while 

 green, save in a few instances, such as the Mercuri-alis porennis ( Doom's Mercury) and 

 the Bryonia dioica (red-berried Bryony) is confined to the leaves and tlie calyx. 

 Red is found most frequently in the corolla, but it appears often in the leaves 

 when decaying ; it also tinges seed vessels and fruits. Black is found in the 

 roots, seeds, and sometimes, as in the Vicia tribe, in the seed vessels when ripe, 

 of which fact it is in such cases the evidence. 



Whatever may be the hue, or the part to which it is usually appropriated, it 

 is ascertained that the colour in plants is generally due to the presence of a sub- 

 stance called chromule, distinct from the sap, which is found in the form of 

 minute grains in the cellular tissue. The common theory of its formation, as 

 physiologists state it, is a chemical one. It is asserted that the carbonic acid gas, 

 which has been absorbed by the plant, is decomposed in the cellular tissue, the 

 oxygen being given oS to the atmosphere, while the pure carbon is retained by the 

 plant, and converted into colouring matter. The researches into human physiology 

 exhibit a case in some degree similar, in the colouring matter of the hair, of the 

 negro's skin, &c. In the plant, this process of manufacturing chromule goes on 

 most actively under the influence of sunlight. That part of the stem of a grass, 

 or of the leaf-stalk of an Arum, for example, which is hidden by the soil or 

 the surrounding grass, is always white. By imitating this natural process, the 

 gardener blanches celery, or quickens the hearting of celery or cabbage. Dry 

 plants become succulent in darkness, owing to the imbibed moisture not being 

 so readily carried oflE by evaporation ; and, which is less easily explicable, acrid, 

 and even poisonous plants, may be rendered innocuous by the same process of 

 " blanching." This would seem to show that the constituent of chromule is not 

 pure carbon, but varies somewhat according to the constituents of the plant in 

 which it is formed. 



This conjecture may, too, help to explain the great difficulty of the chemical 

 theory, viz., the production of a green hue in the leaves, and of a variety of other 

 colours in the flowers of the same plant. May it not be because there are not 

 only individual elements in different species, but distinct secretions in different 

 organs of the same plant, which chemically modify the ctiromule ? This, of 

 course, you will take as merely my conjecture. 



The chronological changes of colour are explained satisfactorily. To quote 

 the valuable little work of Messrs. Chambers on " Vegetable Physiology," " It 

 is found that when the leaves first expand, and are of the brightest green, the 

 grains of chromule are always surp^unded by a thin film of gluten, the principal 

 ingredient in which is nitrogpri. In autumn, the gluten and carbon generally 

 have both disappeared, particularly in plants which contain a notable amount of 



