ГУ ог. 4 
176 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
MicrocHEMICAL TESTS 
In attempting the solution of a pathological problem by 
microchemical methods one must bear in mind that even indi- 
vidual healthy plants may, under apparently normal condi- 
tions, vary in their chemical composition. Differences in en- 
vironmental factors, though relatively imperceptible, may be 
sufficient to change, for example, the acidity of plant tissues, 
while the more obvious effect of shade or decrease of illum- 
ination is evidenced in a decreased a lation of fats, сат- 
bohydrates, and proteins. For this reason it is important 
that comparative analyses be made, not only on the same 
plant but on the same leaf and on adjacent areas. The micro- 
chemical methods now available are the results of investiga- 
tions on normal healthy tissues, and some may think that 
their application to pathological tissues is unwarranted, and 
that the results obtained should therefore be interpreted with 
considerable reserve until the general application of the tests 
has been more definitely established. Microchemical tests, 
especially those outlined in the works of Molisch (713) and 
Tunmann (713), have arisen from innumerable tests on plants 
distributed throughout the vegetable kingdom. If their posi- 
tion is justified in the study of healthy tissue, they may well 
find a place in pathology. 
The results obtained from a microchemical study should, 
whenever possible, be verified by macrochemical analyses or 
by other appropriate methods, as we are able to do for nitro- 
gen by means of the Folin micro-Kjeldahl method. Consid- 
erable difficulty, however, will be experienced in getting 
enough material from well-differentiated areas of any one leaf 
or part of a leaf to make macrochemical analyses, and since 
no delicate macrochemical methods for the general analysis 
of plant tissues other than for nitrogen are available, the 
microchemical results reported below will have to suffice for 
the present. The results, furthermore, are not only relative 
as regards the comparison between different tissues, but are 
relative in themselves, since no absolute value can be de- 
termined and one is obliged to rely entirely upon impartial 
