MISSOURI BOTANICAL GARDEN BULLETIN 135 
poison oak, Virginia creeper, and many others. Brown and 
purplish tones are often exhibited by hickory, persimmon, 
and ash. The vegetation that is suddenly cut off by severe 
frost seldom exhibits the best reds. Climatic influences are 
important, and it is clear that regions with a fairly high 
humidity and cool nights, as the autumn approaches, are 
those in which the highest coloration is attained. Neverthe- 
less, similar pigmentation may be developed (in those plants 
capable of it) almost any season. In the middle of the sum- 
mer a branch of hard maple or an isolated shoot of sumac 
may show high coloration. The heightened color is usually 
to be associated with some injury whereby the food materials 
manufactured in the leaves are not conducted away from the 
shoot or branch. 
The production of anthocyanin in plants has been made 
the subject of much experimental study and careful analysis. 
It appears that the abundance of color in plants capable of 
producing it at all is related to the su content, and it 
also appears to be dependent upon oxidation phenomena. 
During the growing season the sugar produced in the leaves 
is rapidly utilized, but in the fall it is not required to such 
an extent in respiration, nor is it conducted away so freely. 
At the same time, the conditions are most satisfactory for 
the oxidation of the pigment mother substance, or chro- 
mogen. The pigment belongs to the group of substances 
chemically known as glucosides, containing glucose or fruit 
sugar as one constituent. It is interesting to note that twigs 
laced in a sugar solution, and under conditions otherwise 
hitorable, have been found to redden conspicuously. 
The red pigments of autumn coloring belong to the same 
group of substances as the pigments of red beets and ore 
grapes, of most red, purple, and blue flowers, and the red 
colors of such summer es plants as many varieties of 
coleus, begonia, croton, and the purple beeches and maples. 
In these last-mentioned foliage plants, however, the red color 
is distinctive of the variety or species practically throughout 
its period of growth, and it is developed so abundantly in 
the cell sap as to completely veil the chlorophyll, The 
simple experiment of plunging a red coleus leaf into boiling 
water for a few minutes is cient to demonstrate that the 
soluble red pigment is removable, and this removal makes 
visible in striking manner the green chlorophyll which is 
insoluble in water. 
The landscape architect uses to advantage shrubs and 
other perennials which offer the Sree of autumn fol- 
a colors, and likewise those—like -the osier dogwood— 
whose twigs are reddened in the fall and remain brilliant 
