Notes . 
165 
of the bud 1 . This is the case also with the single sporangia formed 
on the edge of the prothallus, and probably holds good for the 
groups of sporangia borne on the process. But tracheides may 
occur in the prothallus at a distance from the place of origin of 
buds or sporangia. Putting aside the case of the middle lobe, the 
prothallial nature of which is open to doubt, a large bundle of 
tracheides was found in the substance of a fleshy prothallus of 
a variety of Scolopendrium vu/gare, which bore numerous archegonia 
on the surfaces immediately above and below the tracheides. Elongated 
cells, which resemble sclerenchyma-fibres, occur in the midrib of 
certain frondose Liverworts 2 . A still more instructive example is 
afforded by the presence of tracheides in the massive endosperm of 
certain Cycads 3 . This latter case shows clearly that such elements 
may be formed in the gametophyte to meet a physiological need. 
It seems inadvisable, therefore, to lay stress on the presence of 
tracheides as a means of distinguishing between the two generations, 
and the more so since their occurrence in a portion of the prothallus 
which is about to bear a bud or sporangia can be recognized as 
a physiological advantage. Such means of procuring a sufficient 
water-supply may be a necessary preliminary to the development of 
a young sporophyte or a group of sporangia. 
Lastly, it remains to consider the view to be taken of the presence 
of the characteristic reproductive organs of the asexual generation 
upon the gametophyte, and to consider its bearing upon the nature 
of alternation of generations in the Archegoniatae. Since the discovery 
that in certain cases the one generation could arise directly from 
the other without the intervention of the proper reproductive organs, 
such cases have been used in support of the view that the alternation 
in the Archegoniatae was homologous 4 . On the other hand, it has 
been maintained, both on grounds of the exceptional nature of these 
cases of apospory and apogamy, and of comparative phylogeny, that 
the distinction between the two generations was a much deeper 
one ; that the alternation was not homologous, but antithetic 5 . So 
far no case has been recorded in which the proper reproductive 
organs of the one generation were situated upon the other without 
1 Farlow, loc. cit., p. 269. 2 Goebel, Outlines, p. 145. 
3 I am indebted to Professor Bower for this unpublished fact. 
4 Pringsheim, Jahrb. f. Bot., Bd. ix, p. 43. 
5 Bower, Annals of Botany, Vol. iv, p. 347. 
