Yasui. — On the Life-history of Salvinia natans. 477 
The upper small cell forms, by further divisions, the prothallium tissue, 
while the nucleus of the lower large cell multiplies by free nuclear divisions, 
and the nuclei are finally distributed throughout the parietal layer of cyto- 
plasm (Fig. 87). Before the prothallium pushes out from the spore cavity* 
a large cell appears on the upper surface of the prothallium, which is soon 
found to be the initial-cell of an archegonium (Fig. 88). 
The archegonium-initial divides into two by a cross-wall (PI. XLIII, 
Fig. 89), and the upper one is divided longitudinally twice (Figs. 90, 92, 94), 
by walls at right angles to each other, into four cells, every one of which is 
again divided twice transversely (Figs. 94-96). The uppermost four cells 
are cover-cells and the others are neck -cells. 
Almost simultaneously with the first division of the upper cell, the 
lower one divides unequally by means of a curved wall into the smaller neck 
canal-cell and the larger central cell (Figs. 90-93). The central cell now 
divides by a curved cross-wall. The outer small cell is the ventral canal-cell 
and the inner large cell is the egg-cell (Figs. 94, 95). 
Pringsheim gives no statement about the presence of the ventral canal- 
cell, but he seems to have observed it as his figures (Pringsheim ’ 63 , 
PI. XXVI, Fig. 1) and the following statement shows : ‘ So sieht man, wie 
hier beilaufig bemerkt werden mag, den Inhalt der Canalzelle in zwei ver- 
schiedene Massen sich sondern (XXVI, 1), in einen grossen fadigschleimigen 
Klumpen, der die ganze Spitze ausfUllt, und einen kleinen tieferliegenden 
Klumpen, welcher der veranderte Zellkern der Centralzelle zu sein scheint.’ 
The lower segment of the neck canal-cell in the above description may very 
likely represent the ventral canal-cell. 
The nucleus of the neck canal-cell then divides into two, though there 
does not arise any membrane which would separate the nuclei. According 
to Campbell (’ 05 ), in Azolla ‘the neck canal-cell may have its nucleus 
divide,’ but mentions that ‘ this has not yet been observed in Salvinia ’. 
On both sides of this first-formed archegonium, there arise later two to 
four archegonia (Fig. 100). Pringsheim stated that on each female prothal- 
lium usually three archegonia arise, and he also mentions that he has some- 
times seen the prothallium with a great many archegonia, which he attributes 
to the absence of fertilization. I have not been able to observe any pro- 
thallium with such numerous archegonia, as I have made no observation 
by preventing fertilization. 
As already noticed by Pringsheim and later investigators of Salvinia , 
the vegetative cells of the prothallium contain many chlorophyll grains and 
continue to grow, until, after the appearance of the archegonia, they spread 
like wings on both sides of the prothallial tissue where the archegonia 
are located. The prothallium assumes, sooner or later, a dorsi-ventral 
structure, and the archegonia are found on its ventral side (Figs. 99, 100). 
