How to insert text labels to data points (not in the data) using panel.text() in a lattice plot

Question

I created a scatterplot from the data (see rcode and data below). The y-axis shows the mean rate of sapflow measured from the xylem in trees during transpiration and the x-axis shows the mean ambient temperature.

Within the scatterplot, 5 points are shown. Each point shows how mean temperatures affect mean rates of sapflow over a 5 month period (i.e. June-October).

Problem

The first column in the data frame (found below) is called "Date" and consists of 5 rows named "June", "July", "August", "September", and "October".

My overall goal is to label the five data points (i.e. labeled from left to right - data point 1 to data point 5) in the lattice plot (shown below) with text labels denoting these 5 months (i.e. found in column 1 in the data frame provided below) but not to let the text overlap with the trend line so it is easy to read (see the lattice plot below):-

For instance (see lattice plot below):

1. Data Point 1 = labeled June;
2. Data Point 2 = labeled July;
3. Data Point 3 = labeled August;
4. Data Point 4 = labeled Septebmer;
5. Data Point 5 = labeled October;

In response, I created a vector called Data_labels and I tried to label the points in the lattice plot using panel.text() to insert the text labels onto the data points.

However, I keep on getting these types of error messages when using panel.text() in different combinations.

Would anyone be able to help? If so, I would be deeply appreciative

Rcode

 ##Produce the date labels for the plot
      Date_labels<-c("June", "July", 
                     "August", "September", 
                     "October")

##Produce lattice plot
xyplot(Mean_Sapflow~Mean_Temperature, 
               data=Summarised_new_mean_sapflow, 
               col="red",
               pch=19,
               xlab="Temperature (°C)",
               ylab=expression(paste("Sapflow Litres day"^{-1})),
               type=c('p', 'smooth'),                  col.line='blue',
               panel.text(0,0, labels=Data_labels))

Error messages:

       Error in grob(label = label, x = x, y = y, just = just, hjust = 
       hjust,  : 
       object 'Data_labels' not found

Scatterplot

Data:

    structure(list(Date = structure(c(3L, 2L, 1L, 5L, 4L), .Label = c("August", 
"July", "June", "October", "September"), class 
    = "factor"), Mean_Humidity = c(17.6073333333333, 
    21.8006451612903, 18.3896774193548, 14.822, 11.3486666666667), 
        Mean_Radiation = c(263.673333333333, 270.906451612903, 178.98064516129, 
        152.233333333333, 93.6), Mean_Temperature = c(70.5613333333333, 
        61.3306451612903, 71.7335483870968, 72.2136666666667, 81.743
        ), Mean_Sapflow = c(16.067, 23.3567741935484, 22.9416129032258, 
        19.3093333333333, 6.70066666666667)), class = "data.frame", row.names = c(NA, 
    -5L))