41 



ing Arbor Vitoe, Retinispora, Red Cedar, and others assum- 

 ing a yellowish or brownish color. 



Hemlocks and spruces generally retain their verdure in a 

 remarkable degree. The variegated Japanese Honeysuckle 

 has its recent leaves of a yellow color, or green reticulated 

 with yellow. It is only after successive frofit!< in Noveml)er 

 that the yellow is replaced by crimson ! 



Euphorbia Cf/jjarissias, a garden escape, often common 

 by roadsides, also changes only after freezing weather in 

 November, from green, through purple, to a bright orange 

 red ! 



"Chlorophyll during the absorption of light is slowly 

 broken down. If it is decomposed faster than it can be 

 rebuilt by the protoplasm the entire leaf dies." (Prof. I). 

 T. Macdougal). 



"Another causie which may disturb the relation between 

 absorption and transpiration, is the diminished conductivity 

 of woody tissue at low temperature." (Doct. G. L. Good- 

 ale). 



The autunm change of color in foliage, resulting in part 

 from the decomposition of the chlorophyll, in distinction 

 from the screening colors which disappear after a time, indi- 

 cates a loss of vitality and a gradual dying of the leaf. 

 This state can evidently be effected by either drought or 

 frost, as well as by many other causes. In the case of 

 drought, the lack of moisture at the roots prevents the 

 necessar}^ supply of water to the leaves, on account of which 

 the tissues become dried, and the character of the cell con- 

 tents greatly changed. In the case of a frost, the frozen 

 ground, or chilled trunks and twigs, with lessened conduc- 

 tivity, fail to deliver to the leaves an adequate amount of 

 water for transpiration, and the result to the leaf is virtually 

 the same as from drought. 



If the various causes of color-change enumerated in the 

 preceding pages were analyzed, it would be found that the 

 proximate cause in all cases was an insufficient supply of 



