My dear Mr Darwin

I will certainly try to get Passiflora Princeps—

Hooker has sent me a number of flowers from Kew but none of P. pr.—¹ I find no very great differences—but one or two interesting details eg (1) that the length of the upright middle corona is proportioned to the height, position & apertures of the inner one, so as to lead the bee over the knobs of the former to the apertures in the latter:

(2) the apertures in the latter seem also to be correlated to the interior projections, so as to render a straight passage to the nectar impracticable.

(3) as a matter of morphology I think that the process round the column is a first corona: making with the three developed coronas, four in all, whilst the process which forms the nectary in Passiflora, seems to be the base of the next interior corona.

I remarked with interest what Hildebrand says about geraniums— There is a passage about it at p. 28 of his book which you recommended me last year in which he ingeniously suggests that the absence of stamens in the disk flowers of Corymbifers may, be due to this cause—² And I see that I made a note on it suggesting that it was doubtful. considering that in such flowers as Senecio—or Calendula there are an immense number of blossoms lasting throughout the year: and that unless we assume fertilization to take place in the same flower-head, (which is contrary to the hypothesis) there can be very few disk flowers which are not contemporaneous at first opening with mature pistils in other flowers.— This does not touch the case of a specially early or late Geranium or Campanula³

Sincerely yours | T H Farrer

C Darwin Esq^r FRS