A zolla filiculoides , Lain. 157 
the subject, is very incomplete, especially with reference to 
the early stages of the former. Belajeff 1 has published an 
account of the male prothallium of A. filiculoides in a recent 
paper on the male prothallium of the Rhizocarpeae. 
The same methods were used by me in the study of Azolla . 
that I have found most successful in the study of other 
delicate plant-tissues. The material was fixed with a 1 per 
cent, aqueous solution of chromic acid, stained in toto with 
alum-cochineal, and then imbedded in paraffin. After sec- 
tioning, the sections were stained on the slide with Bismarck- 
brown in 70 per cent, alcohol. As yet I have found no other 
method which gives such good results. 
Before considering the development of the sporangia and 
spores it may be well to describe briefly the structure of the 
mature sporophyte. As Strasburger has treated this very 
exhaustively in the memoir referred to, it will not be worth 
while to go much into detail here. The plant is strongly dorsi- 
ventral ; the leaves form two alternating rows completely 
concealing the stem. Each leaf is deeply two-lobed, and in 
the dorsal lobe is a large cavity in which is always found 
a colony of a Nostoc - like plant, Anabaena Azollae. 
The growing-point of the stem is curved upward and back- 
ward, so that longitudinal sections parallel to the surface are 
very difficult to get. The stem grows from a single apical 
cell (PL VII, Figs. 2-4, x ), from which two series of segments 
are cut off with great regularity. Each segment now divides 
into a dorsal and ventral cell, so that a transverse section of the 
stem, just back of the apex, shows usually four cells arranged 
like quadrants of a circle (Fig. 5, I.). From the dorsal cells 
the leaves are developed : from the ventral, the lateral branches 
and roots. An examination of the growing-point of the stem 
shows that it is more or less surrounded by a tangle of 
Anabaena- filaments, and some of them creep into the cavities 
in the young leaves and form the beginning of the colony 
referred to. 
The mother-cell of a leaf is distinguishable by its size and 
1 loc. cit. . 
M 2 
