So BOTANICAL GAZETTE. [ April, 
often surrounded by the pellicle referred to, and the cell sap 
is colored by the characteristic red coloring matter, erythro- 
h 
In the yellow leaf the cell contents are much like those of 
the red leaf, but the cell sap is colorless and the chlorophyll 
masses are stained yellow by xanthophyll. 
hat has been said of red and yellow and brown leaves 
is applicable as well to groups of cells in the case of mottled 
eaves. 
The existence of erythrophyll and xanthophyll in these 
positions, the former in the cell sap, the latter in the solid 
cell contents, is of course well known in a general way. But 
we wish to add an additional fact or two in the explanation 
of these phenomena. Chlorophyll, manufactured constantly 
under the influence of light, is as constantly undergoing 
decomposition by the metabolism 
of the cell. Under ordinary condi- 
tions the manufacture of chloro- 
phyll is sufficient to cover up its 
decomposition and the leaf retains 
its green color. Under certain 
changed conditions, however, such 
as intense light or diminished vital- 
ity, the decomposition of chloro- 
phyll exceeds its manufacture, and 
xanthophyll (probably one of the 
products of its decomposition’) ap- 
pears. In other words, xanthophyll is being formed all the 
re ly €S apparent when the manufacture of 
chlorophyll is checked. The condition of intense sunlight 
Sives us the occasional summer yellowness, while to lowered 
vitality must be attributed the failure of chlorophyll manu- 
facture in the autumn. This lower vitality is brought about 
vy diminution of light, lowering of temperature, and proba- 
; The common notion that frost 
coloration is true only so far as it is 
one of the causes which tends to diminish fie ial of the — 
plant and so the manufacture of chlorophyll. Autumnal col- 
ee hired take place before any frost. Xanthophyll then 
stains the ps masses yellow, which were before 
d bslorad es h fferent 
n 1s brought about in a very differen 
way, as erythrophyll is ibeatanhicea in the leaf "ad stains 
‘Vines’ Physiology of Plants, p. 241, 
