1918] CURRENT LITERATURE II7 
oped forms. WI.Is had concluded that species are not dying out. In con- 
clusion, SINNoTT emphasizes the complexity of the problem and points out the 
many factors involved. e complexity of a problem, however, should 
justify rather than discourage the development of such a theory.—MERLE C. 
COULTER. 
Free ammonia and ammonium salts in plants.—WEEVERS” has made a 
large number of determinations for free ammonia and ammonium salts in 
tissues of various members of the plant kingdom. Tests for ammonium salts 
were made as follows: a portion of the plant material (25 mg.) along with a 
drop of water was placed in the bottom of a collared microscope slide. Some 
powdered magnesia and a wad of cotton bearing a little chloroform were added. 
A cover glass bearing a hanging drop of platinic chloride was then placed on 
the collar. The chloroform killed and rendered the cells permeable, while 
the magnesium oxide liberated the ammonia from the ammonium salt of the 
tissues. The ammonia was detected by the (NH,)2Pt Cls crystals in the 
anging drop. For the detection of free ammonia only the tissue or the tissue 
and the chloroform were added along with the hanging drop. Sodium hydrate 
(20 per cent) could be substituted for magnesia only in case the reaction was 
rapid, for the former liberates ammonia from amides in a few hours at room 
temperature. WEEVERs believes he could estimate closely the relative amount 
of ammonium salts in various tissues by the amount of (NH,).Pt Cle crystals 
formed. His estimates tallied with the quantitative determinations that were 
made in many cases. 
Among phanerogams free ammonia was found only in bacterial nodules. 
In cryptogams it was occasionally found in Hymenomycetes and lichens. 
Ammonium salts were found in all species examined except in some mycotropic 
and insectivorous forms naturally growing on acid moorlands poor in ammo- 
nium salts. Their absence in these forms is apparently related to the nature of 
their protein metabolism and not to nitrogen shortage in the soil, as indicated 
by their behavior in water cultures and by other plants of the same habitat 
bearing ammonium salts. The amount of ammonium salts present in the 
leaves of any plant is apparently independent of their presence in the soil. 
Ammonium salts that are absorbed by the roots from water cultures are 
quickly transformed and do not influence the amount in the leaves. Many 
facts indicate that these salts result from protein metabolism, assimilation, and 
dissimilation. The more vigorous metabolism in any part the more ammonium 
salts are present. Some plants and plant parts are rather rich in ammonium 
salts, bearing as much as 2 per cent; certain sea forms (Noctiluca miliaris) ; 
many hymenomycetes and lichens (excepting lichens on moorlands); certain 
Liliaceae and Cruciferae (onion and cabbage roots), and root nodules of 
*7 WEEVERS, TH., Das Vorkommen des Ammoniaks und der Ammonsalze an - 
Rec. Trav. Bot. Neerland. 13:63-104. 1916. 
