98 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



certainly in a situation in which transpiration can not be 

 very rapid while the suckers are actively growing. 



We come now to consider what causes the suckers of 

 certain redwoods to be white while others are green. It is 

 evident that the white redwoods are not white from etiola- 

 tion, for other suckers similarly situated, and other plants 

 all about, are as green as usual. Nor can lack of iron be 

 the cause, for the same reason. So far as I can see, the 

 only reason for these plants being white is that the leaves 

 form, and attain nearly or quite their full size, at a season 

 when there is insufficient warmth for the formation of 

 chromatophores and chlorophyll pigment, though enough 

 for growth. This is in perfect harmony with Sachs's obser- 

 vation (1864), since extended by Frank (1895), that seed- 

 lings growing and buds unfolding at low temperatures 

 produce leaves yellowish or white, either wholly or in 

 patches. I had occasion to notice this phenomenon par- 

 ticularly during the past winter in the leaves of Bur Clover 

 (Medicago denticiilata Willd;. In December and January 

 there were warmth, moisture, and hght enough for a lush 

 vegetation composed of the common annuals, but the nights 

 were chilly and the days not warm. There was an unusual 

 amount of variegation in the leaves of the common weeds. 

 That there was light enough for chlorophyll formation is 

 evident from the fact that Bur Clovers growing in the labo- 

 ratory had no white or variegated leaves. As Sachs proved 

 by experiment, the plant must have a certain minimum 

 amount of warmth in order to form chlorophyll. This min- 

 imum, higher than the minimum for growth, of course 

 varies with the species. 



The white redwoods growing on the crest near the La 

 Honda road are killed down to the ground each year by the 

 frost. This is evidence of considerable cold. In January 

 of this year (1900), when I visited these white redwoods, 

 they had been frosted down but, buried in the leaf-mould 

 covering the branch of the old stump from which the white 

 redwoods spring, were many buds, healthy, with well formed 

 but perfectly white leaves. On that summit no temperature 



