1887-88.] Colouring Matters of Leaves and Flowers. 291 



in the tissues of the plant, flower-colouring will proceed 

 normally under such conditions. 



It is within the experience of every gardener that coloured 

 foliage plants, such as species of Coleics, Croton, Arum, can be 

 grown most effectively when tlieir roots are " pot bound," or 

 on dry places, that is, with restricted nutrition, not where 

 moisture and a plentiful supply of rich soil will favour vege- 

 tation. Many algse show exactly the same phenomenon. 

 A Chroolcptis, cultivated by Mr Terras, was invariably green 

 when grown in the more nutritive environment of water, but 

 yellow when out of water. Similarly, van Tieghem mentions 

 that Bacillus viridis, though green when in its home of 

 stagnant water, becomes pale in fresh water. 



The colour-changes of autumn and of spring occur also 

 when assimilation is at a minimum, when material already 

 in the plant undergoes further elaboration, active vegetation 

 having ceased in the one case and not commenced in the other. 



We may recognise a definite order in which colour-changes 

 occur, and Mr Grant Allen has also made us acquainted with 

 a similar order indicating increased specialisation, his argu- 

 ments being based on distinct morphological specialisations 

 in the plants accompanying the colour. 



It is only when we have fully recognised the possible 

 effects of such environments as we have been considering, 

 and the different colour-changes which may be definitely 

 associated with certain conditions, that we are in a position 

 to recognise the possibilities of selection and of heredity in 

 perpetuating such colours as are useful, and in taking 

 advantage possibly of the less, certainly of the most, rapid 

 variations resulting from one or another of the causes that 

 we have enumerated. 



Without at present giving any attention to the influence 

 of selection, we may conclude this portion of the subject by 

 enumerating, without special reference to the cause, other 

 natural groups of clearly-defined colour-changes which have 

 been observed in flowers. These have been noticed in 

 individual plants. When they may be distinguished according 

 to the time when they occur, the cause is probably the 

 same in each case. 



(a) There are the quick or slow changes as the flowers 

 expand, e.g., in Pulmonaria, Myosotis, Orohus, &c. 



