_A_d_d _a_n _A_x_i_s _t_o _a _P_l_o_t
	
	     axis(which, at, labels=TRUE, lty="solid",
	             col=par("fg"), cex=1)
	
	_A_r_g_u_m_e_n_t_s:
	
	       which : an integer specifying which side of the plot
	               the axis is to be drawn on.
	
	          at : the points at which tick-marks are to be
	               drawn.
	
	      labels : this can either be a logical value specifying
	               whether (numerical) annotations are to be
	               made at the tickmarks, or a vector of charac-
	               ter strings to be placed at the tickpoints.
	
	         lty : the line texture to be used for the axis.
	
	         col : the color for the axis labels.
	
	         cex : the expansion factor for the axis labels.
	
	_D_e_s_c_r_i_p_t_i_o_n:
	
	     axis adds an axis to an already existing plot.  The
	     axis is placed as follows: 1=below, 2=left, 3=above and
	     4=right.
	
	_E_x_a_m_p_l_e_s:
	
	     plot(1:4, rnorm(4), axes=FALSE)
	     axis(1, 1:4, c("A", "B", "C", "D"))
	     axis(2)