FILICINEM, 
449 
The embryo of Salvtm'a, as long as it is enclosed in the protb allium, forms, as 
we have seen, the segments of its apical cell alternately above and below; but when 
the apex of the stem is exposed in consequence of its elongation, a torsion takes 
place to the extent of about 90°, so that the two rows of alternate segments of the 
apical cell lie right and left, a peculiarity which has also been observed by Hof- 
meister in Pteris aquilina. The first leaf is the scutiform leaf mentioned above, 
which is placed medio-dorsally ; then follow a second and third aerial leaf standing 
singly, after which the definite verticillate arrangement of the leaves at length 
commences at the fourth node ; each whorl thereafter consists of a submerged leaf 
springing on the ventral side (right or left), which at once branches, and forms a 
tuft of long filaments hanging down into the water ; while two other leaves have 
quite flat laminae and spring from the dorsal side, touching the water only with their 
under surface (Fig. 319). These three-leaved whorls alternate, and thus form two 
rows of ventral submerged, and four rows of dorsal aerial leaves. Their succession 
Fig. 315 a.— A the vegetative cone of the stem oi Salvtm'a nutans, represented diagrammatically and looked at from 
above; xx projection of the plane which divides it vertically into a right and left half; the segments are indicated by 
stronger outlines, their divisions by vvfeaker lines ; the succession of the segments is denoted by the letters F — P ; 
diagraiS of the stem with three whorls of leaves, its ventral side indicated by vv ; w the first-formed submerged leaf ; 
L\ the aerial leaf formed next ; Li the second aerial leaf of the same whorl formed last of all between the two first (after 
Pringsheim). 
in age in the whorl, and the position of the whorls (antidromal among themselves), 
are indicated in Fig. 315 a. The node of the stem which produces a whorl of 
leaves is, as was shown by Pringsheim, formed of a transverse disc of the long 
vegetative cone, which in its length (or height) corresponds to a half-segment, while 
each internode corresponds to the whole height of a segment. Each nodal disc, as 
well as each internode, consists of cells of the right and left row of segments of 
different ages ; in Fig. 315 a an internode is formed of the segment ZTon the right 
side, of the anterior half of the older segment, G, and of the posterior half of the 
younger segment, J, on the left side ; the next internode is the product of the whole 
of the left segment, Z, and of the two halves of K and M lying to the right ; the 
intermediate nodal disc which forms the leaves iv, L^, consists, on the other 
hand, of the anterior half of the left older segment J and of the posterior half of the 
right younger segment K\ in the preceding and succeeding node the relationships 
G g 
