Azolla filiculoides , Lam. 1 8 1 
comparatively late. No trace of them can be seen until the 
second leaf is pretty well advanced. There is nothing peculiar 
about their development. Simultaneously in the axis of the 
root and stem, and extending into the centre of the cotyledon, 
a series of longitudinal walls arise that give rise to a thin pro- 
cambium-cylinder. In the axis of this the cells become 
transformed into tracheids with close spiral thickenings in 
their walls. At the point of junction of the primary bundles 
the tracheids are as usual irregular and connect the tracheary 
tissue of the three bundles. No trace of a bundle could be 
detected in the foot. The development of the fibro-vascular 
bundles does not take place until some time after the embryo 
has broken through the prothallium. 
The second root arises close to the base of the second leaf, 
and originates from single epidermal cell in the same way 
that the later ones do (Fig. 70 r'). A rapid growth takes 
place now in all the cells of the embryo, and in the cotyledon 
intercellular spaces are formed, which filling with gases, soon 
cause the young plant to rise to the surface of the water. As 
the embryo breaks through the episporic appendages at the 
top of the spore, these are forced apart, and the top of the 
indusium, which has covered it up to this time, is thrown off. 
The young plant at this stage becomes very easily separated 
from the prothallium, and is often found floating free. At 
this stage the cotyledon forms a sort of bell-shaped sheath, 
opening only in one side by a narrow cleft, and completely 
surrounding the growing-point within. The root is still in- 
conspicuous, and forms merely a slight protuberance on one 
side of the foot which has the form of a short cylindrical 
stalk. The stem is at right angles to the foot, and the suc- 
ceeding leaves form, as in the mature plant, two ranks, over- 
lapping and completely hiding the stem. 
The growth of the first root is limited, and it is distinguished 
from the later ones by peculiar short root-hairs which stand 
out stiffly from it (Fig. 75). The succeeding roots, except the 
second, are formed considerably later, and there does not 
seem to be any determined point at which they arise. 
