448 
VASCULAR CRYPTOGAMS. 
undergoing still further division. The four hypobasal octants give rise to the foot. 
Thus no root is developed at this period, nor is one developed subsequently ; 
Salvinia is absolutely rootless. In order to understand the subsequent processes 
of growth, Fig. 311 must be compared with Fig. 313. The growing embryo 
bursts the prothallium ; from r r r, in Fig. 313 B, arises the foot (caulicle) of 
the young plant (Fig. 311 a)\ from s, Fig. 313 is formed the scutiform leaf 
(Fig. 311 B, b), by the growth of which the terminal bud of the stem becomes 
directed downwards (Fig. 311 A, v). The, epibasal part of the embryo faces the 
anterior side, its hypobasal part the posterior side of the prothallium ; its axis of 
growth lies in the same plane with the median line of the latter. 
The first divisions of the embryo of Marsilia Salvatrix agree in all essential 
points, according to Hanstein's observations and my own, with those of Salvinia; and 
Hanstein states that this is also the case with Pilularia; but in both these genera the 
rudiment of the first root is visible at an early period. The stem in these genera 
also creeps or floats in a horizontal direction from the first, as in Salvinia, and 
forms a number of roots in acropetal succession. Fig. 314 shows the first divisions 
of the embryo of Marsilia Salvatrix. The oospore is divided by a nearly vertical 
basal wall into an anterior (epibasal) larger and a posterior (hypobasal) smaller 
cell : these are divided, as in Salvinia and in Ferns, by a transverse and by a 
median wall, so that the embryo consists of eight cells. Of the four epibasal 
octants, one of the two upper ones becomes the apical cell of the stem, whilst 
the other gives rise to the second leaf (cotyledon) ; from the lower two the first 
leaf (cotyledon) is developed. Of the four hypobasal octants, the lower one, which 
is diametrically opposite to the apical cell of the stem, gives rise to the primary 
root, the other octant at the same level becoming suppressed : the two upper 
ones give rise to the foot (Fig. 314 f). The union between embryo and 
prothallium is brought about by the foot. The apical cell of the stem. Fig. 314 
E, s, thus lies, after the formation of the first three walls, between the anterior 
margins of the first leaf and of the foot. In the stage represented in Fig. 315 
this origin of the first leaf, first root, and foot, may still be recognised from the 
arrangement of the cells. 
The further growth of the three genera, otherwise very different in their habit, 
to which we must add Azolla, although its development has not yet been investigated, 
agrees in maintaining the bilateral structure already manifested in the embryo in 
connection with the decidedly horizontal growth, although, as we shall see, the 
position of the apical cell and of its segments varies. In contrast with Muscineae 
and Equisetacese, but in accordance with Ferns, a leaf is not produced in the Rhizo- 
carpeae from every segment of the stem ; certain of the segments remain sterile, and 
these then go to the formation of internodes. The leaves grow, as in Ferns and 
Ophioglossaceae, basifugally by means of an apical cell which forms two rows of 
alternating segments. Before the development has assumed a constant course, an 
increase of vigour of the young plant takes place, which is shown in the enlarge- 
ment of the leaves and the greater perfection of their forms, as well as in a change 
of their relative positions. But in order to make this clear, it is necessary to 
observe separately Salvinia on the one hand, and the Marsiliaceee {Marsilia and 
Pilularia) on the other. 
