1894. ] Archenema, Protonema and Metanema. 2I 
tubers of Barbula muralis and Trichostomum rigidum are ex- 
amples of this increase; and, of a quite different category, 
the remarkable formation of protonemal chlamydospores by 
Funaria hygrometrica should be mentioned. 
Similarly one notes in metanemata much development in 
form and function, as the ascending series from Riccia and 
Anthoceros is followed. The metanema is, as has been con- 
jectured, very probably a highly specialized gametophore 
which has assumed in connection with its particular reproduc- 
tive functions many improvements in vegetative function 
with their attendant morphological developments. In such 
plants as Preissia or Conocephalus, where the metanema is 
differentiated into vegetative and reproductive branches, one 
seesa reiteration ofthe process by which the metanema was it- 
self differentiated from the protonema. 
The typical metanema of the Muscinezx undergoes a vegeta- 
tive evolution in two directions. It appears either as thallus 
or as leafystem. In the Muscinez, as far as I know, there 
is notruly filamentous metanema. The male prothallium of 
Salvinia, and pollen tubes in general—if they be metanemata 
at all—would furnish examples of the filamentous type. 
is perfectly apparent however that not all of the thalloid me- 
tanemata of the Muscinez are of equal rank. The same is 
true of the leafy-stemmed metanemata. In the Hepatice, 
where both thalloid and leafy-stemmed metanemata are to be 
found, some thalli may be regarded as original while others 
may be considered as derived from leafy stems. Marchantia, 
for example, may, with much reasonableness, be derived from 
a Jungermannia archetype; while Anthoceros, on the other 
hand, may be derived directly from a Coleochzte-like arche- 
type. Theclose genetic union of Marchantia with Ricciathrough 
Boschia and Corsinia, argued by Leitgeb? principally upon 
the basis of sporophytic homologies, is not perhaps to be con- 
Sidered as fully proved. If, on the contrary, Marchantiez 
are to be considered rather as reduced Jungermanniez, the 
Marchantia thallus may be defined as secondary. Thallimay 
therefore arise primarily by the evolution of protonemal 
branches or secondarily by the reduction of a leaf-bearing 
axis. The same suggestions apply to leafy-stemmed metan- 
emata. They may, like Lejeunea, be considered as having 
arisen from thalli the margins of which have become dissected; 
*Leitgeb, Die Marchantieen 49. 1881, 
