1) We want to compile drawgram and drawtree without the X11 graphics option, mainly 
because of concern that on some systems, the compiled binaries may not find
their respective libraries if the Xlibs aren't in the expected place.

In the Makefile, 

#DFLAGS  = $(CFLAGS) -DX
DFLAGS  = $(CFLAGS)

and

#DLIBS  = $(CLIBS)
DLIBS  = $(LIBS)

Note that the default of $(CLIBS) is wrong, because CLIBS is not defined,
whereas LIBS is defined

LIBS    = -lm

When the original DLIBS line is used, the compiler can't find the math libraries.