Acrogyitous Jlingermanniales. 297 
resembles Metzgeria , except that sometimes the protonema is at 
first filamentous and may even undergo branching before giving 
rise to a cell-surface and developing into the adult thallus. In 
Pellia, an ovoid cell-mass is formed by the germination of the 
spore while still within the capsule, a hyaline cell at one end pro¬ 
ducing the first rhizoid when the spore is shed, while the growing- 
point arises from the other end; or both ends may produce a 
rhizoid, while the growing point arises in the middle of the proto¬ 
nema. In Blasia, the cell-mass from which the thallus arises may 
either be produced from the terminal cell of a germ-tube, or the 
latter may be suppressed so that the cell-mass arises directly from the 
spore. The germination of Fossombronia, according to Frau 
Lampa, is somewhat remarkable—the end-cell of the germ-tube 
gives rise to a three-sided apical cell, producing three rows of 
leaves, though the apical cell of the adult plant is two-sided and 
the leaves are in two rows. 
In the Marchantiales, Fegatella resembles Pellia in that the 
spore germinates before leaving the capsule, forming an ovoid 
cell-mass, and [Frau Lampa states that when the multicellular 
spore, or protonema, is set free it grows at first by a three-sided 
apical cell and is cylindrical, but later acquires dorsiventrality and 
gives rise to the adult thallus. The same writer also describes 
the cell-mass formed in various genera of Marchantiales by 
division of the end-cell of the germ-tube, as growing at first by a 
three-sided apical cell and producing three rows of leaves, which 
are especially definite in Preissia. 
As already stated, there are many cases in which the form of 
the Hepatic protonema varies between the two main types—the 
filamentous and the discoid—in the same species. Moreover, it 
has been shown, by Schostakowitsch (74) and others that the 
structure and duration of the protonema can be altered at will by 
controlling the external conditions under which the spore ger¬ 
minates, and that light-intensity is the most important of these 
conditions. For instance, the normally short-lived filamentous 
protonema of Cephalozia, Chiloscyphus, etc., can be cultivated for 
many months in feeble light without producing leafy shoots ; the 
protonema branches freely, like the protonema of a Moss or the 
filamentous vegetative body of Protocephalozia. In the Marchan¬ 
tiales feeble light inhibits the formation of the germ-disc and 
therefore of the adult thallus ; if a germ-disc has been formed, 
reduction in light-intensity causes it to give out filaments, on 
