whats the frequency of the letter i in:
aston, j l, and bradshaw, a d. 1966. evolution in closely adjacent plant populations. ii. agrostis stolonifera in maritime habitats. heredity, 21, 649–664.
bateman, a j. 1947a. contamination of seed crops. ii. wind pollination. heredity, 1, 235–246.
bateman, a j. 1947b. contamination of seed crops. i. insect pollination. j genetics, 48, 257–275.
blair, w f. 1947. variation in shade of pelage colour of local populations of the cactus-mouse (peromyscus eremicus) in the tularosa basin and adjacent areas of southern new mexico. contr lab vert biol, 37, 1–7.
bradshaw, a d. 1959. population differentiation in agrostis tenuis. i. morphological differentiation. new phytol, 58, 208–227.
clausen, j. keck, d d, and hiesey, w m. 1940. experimental studies on the nature of species. i. effect of varied environments on western north american plants. publ carneg inst, no. 520.
clausen, j. keck, d d, and hiesey, w m. 1948. experimental studies on the nature of species. iii. environmental responses of climatic races of achillea. publ carneg inst, no. 581.
day, b, and fisher, r a. 1937. the comparison of variability in populations having unequal means. an example of the analysis of covariance with multiple dependent and independent variates. ann of eugen, vii, 333–348.
grant, v. 1949. pollination systems as isolating mechanisms in angiosperms. evolution, 3, 82–97.
gregor, j w. 1944. the ecotype. biol review, 19, 20–30.
gregor, j w. davey, v m c m, and lang, j m s. 1936. experimental taxonomy. experimental garden technique in relation to the recognition of small taxonomie units. new phytol, 35, 323–350.
gregor, j w, and watson, p j. 1961. ecotypic differentiation. evolution, 15, 166–173.
grime, j p. 1963. factors determining the occurrence of calcifuge species on shallow soils over calcereous substrata. j ecol, 51, 375–390.
heslop harrison, j. 1964. forty years of genecology in advances of ecological research 2. academic press.
iman, a g, and allard, r w. 1965. population studies in predominantly self-pollinated species. vi. genetic variability between and within natural populations of wild oats from differing habitats in california. genetics, 51, 49–62.
jain, s k, and bradshaw, a d. 1966. evolution in closely adjacent plant populations. 1. the evidence and its theoretical analysis. heredity, 20, 407–441.
kruckeberg, a r. 1951. intraspecific variability in the response of certain native plant species to serpentine soil. amer journ bot, 38, 408–418.
mcneilly, t. 1968. evolution in closely adjacent plant populations. iii. agrostis tenuis on a small copper mine. heredity, 23, 99–108.
mayr, e. 1947. ecological factors in speciation. evolution, 1, 263–288.
stebbins, g l. 1950. variation and evolution in plants. new york, columbia university press.
thoday, j m, and boam, t b. 1959. effects of disruptive selection. ii. polymorphism and divergence without isolation. heredity, 13, 205–218.
turesson, g. 1922. the genotypical response of the plant species to the habitat. hereditas, 3, 211–350.
waddington, g h. 1953. genetic assimilation of an acquired character. evolution, 7, 118–126.
wilkins, d a. 1960. the measurement and genetical analysis of lead tolerance in festuca ovina. rep scot plant breed stat, 85–98.

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There are two hundred and sixteen "i"s in the text you provided.
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