Examples of Constant Races. 81 
occur. Similarly Scnccio Jacobaca has a Forma radiata 
and a F. discoidea 1 (Figs. 8 and 9) both of which grow 
in this country and are absolutely constant. The Discoi- 
deus grows in thousands of specimens in the dunes in 
the province of North Holland; but the Forma radiata 
grows equally abundantly in South Holland; both are 
amongst the commonest and most widely distributed spe- 
cies of our flora. For twenty and more years I have had 
them under observation, and never saw any trace of ad- 
mixture or reversion ; the two varieties were always ab- 
solutely pure in the respective localities. Of late, how- 
ever, there have been some cases of intermingling near 
the limits of their areas, probably as the result of seed 
transportation. The two sorts can therefore be regarded 
as absolutely constant. 2 Matricaria Chamomilla discoi- 
dea 3 has proved equally constant in my experimental 
garden, but MURR mentions the occasional occurrence of 
heads with ravs. 4 In 1897 I raised from the seeds of a 
j 
single plant of M. discoidea 575 plants, all of which were 
without ligulate florets. On these I only harvested the 
seeds of the weakest branches of the higher orders and 
raised 460 plants in 1898, all of which again were with- 
1 See Vol. I, p. 196. 
2 A valuable summary dealing with this point is given by. J . 
MURR, Strahllosc Bliltlien bei heimischen Kompositen, Deutsche Bot. 
Monatsschr., Vol. 14, 1896, pp. 161-164. See also Botan. Jahrcsber., 
T. 24, 2, p. n, where rare instances of forms with rays belonging 
to normally discoid species and rayless flowers on normally radiata 
forms, are given. I cite Senecio Jacobaea as an instance of the latter, 
in opposition to the observations given in the text. An attempt to 
discriminate half races amongst these forms (See 3, p. 18) would 
probably lead to valuable results. 
3 For an account of the rapid spread of this form in Norway see 
JENS HOLMBOE, Nogle Ugraesplanters Invandring i Norge, 1900. 
Nyt Magaz. f. Natitrv., Vol. XXXVIII, p. 187 (with map). The 
variety is there also fully constant. 
4 J. MURR, loc. at., pp. 161-164. 
