APRIL. 77 



carry the decaying vegetable matter into the soil, where it 

 tends still further to decompose the mineral matters of 

 which the soil is mainly composed. 



The withdrawal of the utilisable food materials present 

 in the leaf is usually associated with a marked change of 

 colour, the green being replaced by tints of yellow, brown, 

 and red. These alterations of colour are not conspicuously 

 marked in the New Zealand flora, nor are they as a general 

 rule very noticeable in evergreen plants. But the mountain 

 ribbonwood turns yellow, the Fuchsia purplish or brown, 

 while the large leaves of the rangiora (Brachy glottis 

 Ranglora) become beautifully veined with red and purple. 

 It is in the north temperate zone, and especially among 

 the North American and Japanese plants, that the brilliant 

 autumn tints are so conspicuous. There is no reason to 

 believe that these colours are always specially developed at 

 the approach of autumn. The pigments which cause them 

 may be and possibly are normally present in the living 

 plant, most of them perhaps hardly distinguishable in 

 composition from the green colouring matter of the leaves, 

 but all of them masked by the preponderance of the green 

 chlorophyll. In all the young cells of growing plants there 

 occur minute colourless bodies which are technically known 

 as chloroplasts carriers, as it were, of colouring matter, so 

 called because under suitable conditions they develop into 

 coloured bodies. What these conditions are we only know 

 in part. Sunlight seems to be necessary, though some 

 plants can produce their pigment in dense shade, as 

 happens in many ferns and mosses, while others produce 

 it in their seeds. But light does not always produce a 

 green colour, for we know that many plants show natural 

 modifications of red, yellow, brown, and even white, a fact 

 which horticulturists take advantage of to cultivate silver, 

 golden, and variegated races of foliage plants. In flowers, 

 also, by the unconscious selective action of countless genera- 

 tions of insects, the bright hues which so charm our eyes 

 have been developed. The materials were there, but they 

 required selective action to cause them to so preponderate 

 as to produce the prevalent colours of the various flowers. 



