492 BOTANICAL GAZETTE [JUNE 
temperatures, but considerably above the freezing point, induce red colora- 
tion. Alpine leaves are more highly colored than leaves from the lowlands 
because of low night temperatures and increased light intensity. The red 
coloration in many winter leaves is due to an increase of sugar at the expense 
of starch, a condition that is brought about by low temperatures. Cultivation 
in sugar solutions as a rule produced coloration only in those plants in which 
colored cell sap, when present, occurs in the mesophy!]. Plants that have 
red sap in the epidermis failed to respond to sugar solutions. The redden- 
ing of many fruits and the deeper coloration of alpine flowers may be due to 
the change of starch to sugar. ? 
Overton thinks that the red pigment is a glucoside or some nearly 
related compound. The cells which contain the colored cell sap often have 
tannins present, whereas in many plants that showed no coloration there is 
no tannin, The precipitates thrown down by coffein and antipyrin resemble 
those of the tannins, and the author concludes that one of the constituents of 
the red pigment is a tannic acid. The chemical nature of the pigment 
doubtless varies considerably in different plant groups. 
The paper closes with a review of studies on red cell sap, giving great 
credit to the pioneer work of von Mohl. Wigand long ago associated the red 
color with tannins. Although Overton says little as to the ecological signifi- 
cance of red colors, he inclines to Stahl’s view that they increase the avail- 
able heat of the plant and thus favor nutrition. He thinks it possible that 
red colors may have been produced as an adaptation to unfavorable condi- 
tions by means of natural selection — H. C. CowLes 
ITEMS OF TAXONOMIC interest are as follows: F. KRANZLIN has com- 
pleted (Engler’s Bot. Jahrb. 26: 449-502. 1899) his account of Lehmann’s 
Orchidacez from Central and South America, in this last fascicle describing 
about seventy-five new species and three new genera (Otopetalum, Neoleh- 
mannia, Pterostemma).—F. Pax (ibid. 503-508) has published Lehmann’s 
South American Euphorbiacee, describing nine new species.—A. ENGLER 
(2éd@. 509-572) has published his ninth installment of revisions of the genera 
of Aracez, which contains Philodendron with 167 species, twenty-six of which 
are new, and Dieffenbachia, with eighteen species, one being new.— F. 
BUCHENAU discusses Ule’s Brazilian Juncacez (#b¢d. 573-579), and also the 
genus Tropzolum (24d. 580-588).—P. DieTEL and F. W. HEGER (iid. 
27:1-16, 1899) have published their third paper on Chilean Uredinacee, 
proposing Mzkronegeria as a new genus.—R. PILGER (i6id. 17-36) in pub- 
lishing Lehmann’s and Stiibel’s South American Graminez describe numer- 
ous new species.—A. ENGLER’S studies of the African flora have reached 
the eighteenth number (zééd¢. 37-237), which contains the following contribu- 
tions: G. Lopriore, on Amarantacez, in which twenty-two new species are 
described, a new genus Sercostachys proposed, and Sericorema and Cypho- 
