6. _Rainfall._--Twelve years is much too short a period to give a trustworthy mean for such a variable element of climate as rainfall, and five stations are much too few to deduce an average from for Hertfordshire. The average rainfall at a varying number of stations for the sixty years 1840 to 1899 (from one station in the first decade of this period to twenty stations in the last decade) was 26.15 inches. In the driest year (1854) 17.67 inches fell, and in the wettest (1852) 37.57 inches. Spring has 5.40 inches, summer 6.97, autumn 7.87, and winter 5.91. The driest months are February and March, each with a mean of 1.65 inch; April is but very little wetter, having 1.69. The wettest month is October, with 2.96 inches, and the next is November with 2.56. The mean number of days of rain in the year, that is of days on which at least 0.01 inch fell, for the thirty years 1870-99, was 167. Autumn and winter have each about six more wet days than spring and summer. The rainfall is greatly affected by the form of the ground, the southern and western hills attracting the rain, which chiefly comes from the S.W., so greatly that with a mean annual fall of about 26 inches there is a difference of 31/2 inches between that of the river-basin of the Colne on the W. and that of the river-basin of the Lea on the E., the former having 28 inches and the latter 241/2. The small portion of the river-basin of the Great Ouse which is within our area has rather less rain than the average for the county. IV. FLORA AND FAUNA In his _Cybele Britannica_, H. C. Watson divided Britain into eighteen botanical provinces of which the Thames and the Ouse occupy the whole of the S.E. of England. The greater part of Hertfordshire is in the Thames province and a small portion in the N. is in that of the Ouse. In Pryor's _Flora of Hertfordshire_, published by the Hertfordshire Natural History Society in 1887, which should be referred to for full information on the botany of the county, these botanical provinces are again divided into districts, the Ouse into (1) Cam, (2) Ivel; and the Thames into (3) Thame, (4) Colne, (5) Brent, (6) Lea; both the larger provinces and the smaller districts thus being founded on the natural divisions of a country, drainage areas or catchment basins. In the following brief notes a few of the rarer or more interesting flowering plants of each district are enumerated. 1. _The Cam._--This is the most northern district. It is almost entirely on the Chalk and is very bare of trees. The few plants which are restricted to it are very rare. A meadow-rue, _Thalictrum Jacquinianum_, and the cat's foot (_Antennaria dioica_) occur only on Royston and Therfield Heaths; _Alisma ranunculoides_ and _Potamogeton coloratus_ only on Ashwell Common; and of the great burnet (_Poterium officinale_) the sole record is that of a plant gathered near Ashwell in 1840.