CHAPTER XXII 



PLANTS VALUABLE BECAUSE OF THE AUTUMN 

 COLOURATION OF THE LEAVES 



One of the most charming features of our northern landscapes, es- 

 pecially through the northeastern United States where such a great 

 variety of deciduous trees are indigenous, is the autumn colouration of 

 the foHage. During the normal growing seasons, when ample rains 

 have fallen and the trees are full with sap at the end of the season, the 

 autumn colours are much more vivid than during a dry season. 



It is extremely important in designing landscape plantings that 

 thought should be given to the fruiting effects during the fall and 

 winter months and also to the autumn colours of the foliage of our trees 

 and shrubs. A small touch of colour in the border shrub plantings of 

 the average lawn is usually the diflference between an uninteresting 

 and an interesting planting at that season of the year. Every planting 

 should have introduced into it a few plants which, if not valuable for 

 their fruiting and flowering characteristics, will produce a touch of 

 colour as accents to relieve the monotony of the dead greens and 

 browns during late September and October. 



Autumn colouration is the result of an interesting physiological 

 function within the plant. Contrary to the average opinion that 

 autumn colour is the result of sharp freezes, the presence of frost 

 serves but in a sHght degree to hasten this colouring, because the 

 degree of cold necessary to produce a freeze further retards the flow 

 of any sap. The production of the vivid autumn colours is caused by 

 a devitalized or increasingly dormant condition of the plant. The 

 lessened flow of new sap to the leaves, caused by the formatioa of 

 corky tissue at the extreme base of the leaf to cover and protect the 

 leaf scar during the winter months, results in a chemical reaction 

 of the acids within the leaf itself. The results of this chemical re- 

 action are evident in the autumn colours. The factors determining 

 the kind and degree of autumn colouration is the presence of different 



171 



