Cer atop ter is thalictroides , (L.) 1 1 7 
the fertile leaves of Ceratopteris , which curl over the sporangia 
forming a kind of pod, to the sporocarp of Marsilia . The 
leaves which are formed first in the young plants of both are 
also very similar, being simple and spatulate in shape. In 
both plants the stem grows by a three-sided apical cell, 
though in Ceratopteris the actual apex is much narrower than 
in Marsilia , and in general appearance is much more like the 
apex of the stem in Salvinia. In Salvinia , however, the 
apical cell is two- not three-sided, though Leitgeb 1 states 
that in the very early stages a three-sided apical cell is found. 
The vascular system again in Ceratopteris is polystelic, in 
Marsilia it is tubular with an inner and an outer endodermis. 
Taken as a whole Ceratopteris has much stronger affinities 
with the Polypodiaceae than with the Marsiliaceae, but in any 
case it is a divergent form, though many of its peculiarities 
can be directly traced to its manner of life. 
The differences met with in the anatomical structure are 
not enough to place the Parkeriaceae as an order distinct 
from the Polypodiaceae, but the resemblances on the other 
hand are strong enough to admit of their being ranked as 
a sub-order of this group of Ferns. 
« 
Summary. 
The chief points of interest may now be summarized. 
1. Ceratopteris thalictroides is an annual aquatic Fern with 
marked anatomical modifications in correlation with its aquatic 
manner of life. 
2. The stem is much reduced, fertile and sterile leaves are 
present, and the later roots are developed from the bases of 
the petioles. 
3. The steles in the stem and leaves are markedly bi- 
collateral. 
4. In the stem an outer circle of large steles is found, 
within which small, feebly developed steles are scattered 
irregularly. 
5. The vascular bundles of the stem and of the first few 
1 Leitgeb : cf. Schenk, 1881, p. 216 . 
