MISSOURI BOTANICAL GARDEN BULLETIN 153 
_ The Garden contains a number of plants for which the 
internal temperature of leaves, resulting from the absorption 
of radiant energy, has been definitely determined. It has 
been found that during winter the leaves of the Austrian 
pine (Pinus Laricio var. austriaca) will, under brilliant 
Ulumination, attain a temperature from 2-10°C. higher than 
the surrounding air, the temperature of which may be as 
low as —15°C. Even diffuse light, according to its inten- 
sity, will raise the temperature from 0.5-2°C. Leaves from 
tropical plants, such as the cucumber-tree (Magnolia sphen- 
ocarpa) and the three-seeded mercury (Acalypha tricolor) 
will, under full illumination, attain a temperature from 
10-16° above that of the surrounding air, or an actual tem- 
perature as high as 43°C. This is of interest Since the 
lethal temperature for living material or protoplasm is ap- 
proximately 50°C. 
The internal temperature is greatly influenced by external 
factors such as humidity and air currents, but also, and this 
is of primary interest here, by the internal factor of pig- 
mentation. The yellow leaves of Codiaeum variegatum attain 
a temperature 8°C. above that of the surrounding air, while 
the green leaves of the same plant reach a temperature 
11° above that of the atmosphere. Similarly, the internal 
oo See of green and red leaves of variegated caladiums 
is about 4°C. higher than that attained by green and white 
leaves of similar plants. The difference, of course, is 
attributed to the higher absorptive power of the more pig- 
mented leaves. Similarly, young leaves of the cacao tree 
(Theobroma Cacao), which are of a red color due to their — 
high content of the red coloring matter, anthocyanin, may 
attain a temperature 3 or 4°C. higher than that of older 
green leaves relatively poor in anthocyanin. The internal 
temperature attained by thin leaves is practically the same 
as that attained by thick or fleshy leaves, but the latter reach 
their temperature more slowly and, bane influenced less 
easily by breezes, retain their temperature longer and more 
constantly. 
LANDSCAPE ARCHITECTURE EXHIBIT 
In an effort to stimulate interest in landscape architecture 
there will be held in the Museum of the Garden, during the 
month of October, an exhibition of plans, drawings, models, 
and photographs of some of the best of the recent —— 
developments in this country. This exhibition will be under 
the management of the erican Society of Landscape 
Architects and of the Missouri Botanical Garden. Several 
