This paper presents the results of the analysis of 10 years of information 1957-1966 on three phases-- begin, peak and end bloom-- of the purple common lilac (Syringa vulgaris L.) using data recorded at approximately 1,000 locations throughout the Western Region of the United States. The pattern of geographical advance of the various bloom phases is determined by both a manual mapping procedure developed by the author and by standard statistical methods. Manually drawn isophanes for the various elevations for begin bloom phase are based entirely upon the first 5 years of record, 1957-1961. A Zones of Adjustment map to convert the 5-year equal level maps to the 10-year 1957-1966 normal is also manually drawn. Statistical analyses to ascertain the geographical pattern of advance were made for begin bloom phase for the 5-year period and for all three bloom phases for the 10-year period. Both the manual and statistical analyses indicate a very definite pattern of geographical advance of begin bloom phase of the lilac which is characterized by the Early Ridge. Statistical analyses of all three phases indicate a parallel geographical advance of the three phases with average regional time displacement of about 10 days from begin to peak bloom and 10 days between peak and end bloom. Only the eastern third of the Western Region corresponds closely with Hopkins' Bioclimatic Law. A measure of temporal variation of dates of bloom for each of all three phases indicate a parallel geographical advance of the three phases with average regional time displacement of about 10 days from begin to peak bloom and 10 days between peak and end bloom. Only the eastern third of the Western Region corresponds closely with Hopkins' Bioclimatic Law. A measure of temporal variation of dates of bloom for each of the three phases was determined by computing standard deviations for every station having at least 5 years of record. A map was drawn showing the temporal variability of begin bloom phase throughout the Western Region. Medians of standard deviations for stat ions within each state were also determined. Large differences in standard deviation prevail throughout the region with a general tendency for variability to be highest in the southeastern part of the region and lowest in northeastern areas. A comparison is made between the normal dates of occurrence of bloom phases and temperature data throughout the Western Region. This is achieved by comparing isophanal and isothermal charts and by statistical analysis of data at 360 stations where both phenological and temperature records are available. Comparison of isophanal patterns of equal-level isophanal maps and isotherms at given elevations ( or pressure lvels) on given dates indicate very similar patterns; both are characterized by the Early Ridge. Statistical Analyses of mean begin bloom dates and monthly mean maximum and minimum temperatures indicate that about 90 percent of the variance of bloom dates can be accounted for by maximum and minimum temperature measurements.