Morfologia fiorale embriologia ed embriog in Leontopodium alpinum Cass. var. α typicum fiori e Paoletti

Abstract

FLOWER MORPHOLOGY, EMBRYOLOGY AND EMBRYOGENESIS OF LEONTOPODIUM ALPINUM CASS. VAR. α TYPICUM FIORI E PAOLETTI. — The present work has been carried on with capitules of L. alpinum var. α typicum, included and dissected, differing thus from the previous research which is also summarised (BEAUVERD 1909 a e b, 1910, 1012, 1913 a e b, 1914).

The results are the following: all capitules of the same corymb of this species have the same structure, differing eventually in details. Generally they show outwards a few female flowers, inwards a relevant number of pseudohermaphrodite flowers (the sterile hermaphrodite of BEAUVERD). They are therefore subdioecious capitules with tendency to reduce the already scarce number of female flowers. Both female and pseudohermaphrodite flowers have been extensively described. Some rare hermaphrodite flowers with ovules and anthers, and very rare subhermaphrodite without ovules and empty or almost empty anthers have been also observed.

On the same material, embryological and embryogenetical research has been carried out: from it results that the microsporogenesis proceeds normally, without degeneration. The megasporogenesis and the development of the female gametophyte and the formation of an 8-nucleate have been observed and also several cases of poliantiopody. Many gamethophytes at this stage degenerate; the others develop particularly transversally; the antipodes completely degenerate and the secondary nucleus and the egg cell reach remarkable size. Synergids at this stage appear more or less completely fessurate, in their micropilar part.

Fertilisation occurs through porogamy, the zygote producing a bicellular proembryo which goes on dividing while the nucleus of the endosperm forms a cellular albumen.

The embryological and embryogenetical observations do not completely agree with those made by SOKOLOWSKA-KULCZYCKA (1959) on specimens of L. alpinum collected on the Tatra mountains (Carpathian Mts.), where the tetrad often degenerates and only exceptionally brings to the constitution of an aphid gamethophyte. More frequently apomixis has been observed, which implies a parthenogenetical development of the egg cell.