Good cytological evidence has been adduced in favor of both theories, but further investigation is necessary before any definite conclusion can be arrived at.
The cytological evidence for this appears to be made stronger for animal than for plant cells.
Xxxviii.; Meyer, Untersuchungen fiber die Starke-Kdrner (J ena, 1895); Montgomery, Comparative Cytological Studies, with especial regard to the Morphology of the Nucleolus, Journ.
Lxxii.; Wager and Peniston, Cytological Observations on the Yeast Plant, Ann.
7, from which it will be seen that the cytological details are very complex.
4, D), with peculiar cytological differentiation, may be only sub-species; T.
Cytological details of nuclear behaviour among the lichens are, however, difficult to obtain owing 'to the slow growth of these forms and the often refractory t' nature of the material in the matter of preparation for microscopical ex amination.
The cytological details of development of the perithecia are not well known; most of them appear to develop their ascogenous hyphae in an apogamous way without any connexion with an ascogonium.
It is by means of the cytological evidence, however, that this problem will finally be solved.
And since this rule has been found to hold good for all the archegoniate series and also for the flowering plants where, however, the gametophyte generation has become so extremely reduced as to be only with difficulty discerned, it is natural that when alternation of generation is stated to occur in any group of Thallophyta it should be required that the cytological evidence should support the view.
A cytological difference of great importance between the two generations can only be mentioned in passing.
The genus Nemalion has been recently investigated by Wolfe with the object of examining the cytological evidence.
Latterly, however, as the result of the cytological investigations of Mottier and Lloyd Williams, great advance has been made in our knowledge of the conditions existing in Dictyota.