North American species of Lactarius / L. R. Hesler, Alexander H. Smith.

The Basidiocarp

33

eral, the characteristic change is to some shade of red to reddish cinnamon with a few species not staining and some going directly to brown.
In subgenus Lactarius the latex appears to be bright colored as it is
exuded (carrot color, red, purplish, or blue). If one holds a thin pileus
against a light, some evidence of colored lactifers can at times be seen
and it is assumed that their content (the latex) is colored as it is formed in
the basidiocarp. This aspect of the problem needs further study since the
problem of age of the basidiocarp may be important. In subgenus
Lactarius, however, if the latex stains immediately to carrot color
from an originally white state, it must be kept in mind that in many variants
cut areas also slowly stain dark red or purple-red in addition. Lastly,
most species in the subgenus slowly develop green stains. In some these
are prompt in appearance, and in some they apparently do not develop.
The green stains, when present, do not appear to be associated with a
change in the color of the latex.
In the section Atroviridi, the color change to dull olive and the
staining to olive or olive-brown seem to be a single progressive reaction. Difficult problems arise in that at times a change in color takes
place but on standing the droplets fade out to pallid. We have some
unsolved problems involving this pattern of behavior. A difficulty
also arises in the interpretation of dried specimens: On standing in
the herbarium over the years, is the present color of dried latex
globules of taxonomic significance? Our observations as here recorded were from fresh material unless otherwise stated.
Color stains from injury to tissues are reliable at the species
level at times (see L. argillaceifolius), and not so reliable in others
(see L. cinereus and its var. fagetorum). In the present state of our
knowledge, each species must be evaluated separately relative to the
taxonomic value of stains as these are present when the collection is
made or develop after injury. Nondescript discolorations are the least
significant especially if present at the time of collection since one is
never sure of their history. Those which are observed to develop on
injured areas in less than an hour are likely to be significant.
In our study, we have found that in subgenus Russularia two
types of latex are taxonomically significant: milk-white and waterlike. These should be observed on young basidiocarps since it is a common occurrence for a milk-white latex to be whey-like (a hyaline
liquid with white particles in it). In old specimens which feature a
water-like latex when young, the latex may simply appear to be absent. Also, many agarics in various families will exude a hyaline liquid
when the apex of the stipe is cut with a sharp razor. For a Lactarius,
the heteromerous tissue of the stipe will nearly always be distinctive.
Some additional odd color changes or staining reactions are