Azolla filiculoides, Lam. 177 
eight to ten is not at all uncommon. Sometimes, in very- 
old prothallia little elevations are formed projecting upward 
between the older archegonia, and upon these small archegonia 
are developed. 
To judge from Berggren’s 1 figures of A. caroliniana , the 
prothallium in that species is decidedly larger than in 
A. filiculoides, but the archegonia are much less numerous. 
The Embryo. 
Berggren made out correctly the first divisions in the 
embryo, but did not trace in detail any but the very earliest 
ones, and his figures, as in the case of the prothallium are too 
schematic to show the cell-arrangement with any degree of 
accuracy. 
The fertilized egg, previous to its first division, elongates 
vertically. The first, or basal wall, is usually horizontal 2 , 
instead of vertical as in all the other Leptosporangiatae yet 
investigated. In a very few cases (Fig. 65), the basal wall 
was nearly vertical, but this was exceptional. From the 
upper cell the cotyledon and stem arise ; from the lower, the 
foot and first root. Thus the position of the primary organs 
of the embryo is the same with reference to the basal wall, as 
in the other Leptosporangiates, but different as regards the 
archegonium. 
The next divisions, as in other cases, divide the embryo 
into four nearly equal cells. These quadrant-walls (II) do 
not always arise simultaneously. In the only case where 
a three-celled embryo was found by me, the upper cell was 
divided. Berggren 3 states that in A. caroliniana , it is the 
lower cell that first divides. Probably it is not always the 
same one. The formation of the quadrant-walls determines 
the primary organs. In the upper cell one quadrant gives 
rise to the stem, and one to the cotyledon ; and of the two 
1 loc. cit. Figs. 4-16. 
2 That is, assuming ttie axis of the archegonium to be vertical. 
3 loc. cit. p. 4. 
