94 



than white or yellow of the same age in the same bed ; and 

 that the latter close earliest at the approach of a cold storm. 

 This appears to be due to the difference of temperature in 

 the flower; the white requiring most heat, the yellow less, 

 and the red least. The pink Cornus florida blooms a little 

 earlier than the white. 



Newbigin states that "the red parts of plants absorb 1.82 

 per cent, more heat than green parts." 



Another observation may be worth noting in this connec- 

 tion, viz. : I have remarked that in the Southern States 

 there is a preponderance of yellow flowered si)ecies in sev- 

 eral genera which are common to both the North and the 

 South. Following is a partial list : 



The species descril^ed by Gray as greenish, cream color. 

 Chapman calls pale yellow. 



California furnishes yellow Iris, yellow Lupinus, Esch- 

 scholtzia, Calochortus, etc. DelpJiinimn cardinale and D. 

 nudkaule have orange or scarlet sepals or })artly yellow 

 petals, while Northern species are })urple. It would not be 

 at all improbable that some yellow-flowered species originat- 

 ing in Southern climates should on spreading farther 

 North become flushed with red or purple. 



