PLANTS VALUABLE BECAUSE OF THE AUTUMN COLOURATION OF THE LEAVES : Page 449

Autumn colouration is the result of an interesting physiologicalfunction within the plant. Contrary to the average opinion thatautumn colour is the result of sharp freezes, the presence of frostserves but in a slight degree to hasten this colouring, because thedegree of cold necessary to produce a freeze further retards the flowof any sap. The production of the vivid autumn colours is caused bya devitalized or increasingly dormant condition of the plant. Thelessened flow of new sap to the leaves, caused by the formation ofcorky tissue at the extreme base of the leaf to cover and protect theleaf scar during the winter months, results in a chemical reactionof the acids within the leaf itself. The results of this chemical re-action are evident in the autumn colours. The factors determiningthe kind and degree of autumn colouration is the presence of different,