The Morphology of Ruppia Maritima. 105 
sheath “more or less short” at the base of the root, but does not 
give a detailed account of it, so that its nature is not entirely clear. 
This is, however, probably a coleorrhiza. 
According to Sachs (1875, p. 143) in grasses 
and some other Phanerogams, the first root arises 
so deep in the interior of the embryonal substance 
that in the fully developed embryo of the ripe seed 
it is enclosed by a thick, sac-like layer of tissue, 
which is ruptured on germination and is known 
by the name of “ root sheath (coleorrhiza).” Similar 
formations occur also in the first secondary roots 
of the germinating plants of Alum cepa, and 
occasionally elsewhere. 
The coleorrhiza! in Ruppia, which is found on 
all the adventitious roots, is of entirely different 
nature. Its development can be observed at all 
the early stages of the growth of the root. The 
first indication of it appears during the origin of 
the young root within the stem. As the young 
root develops and appears in the stem cortex, a 
change in character takes place in certain of the > 
epidermal cells of the stem, and in a few in the sub- 
epidermal layers, which lie inthe regionwhence the 
Barge Figure 22.— Dia- 
root would naturally emerge. These cells become erammatic repres- 
filled with protoplasm, their nuclei enlarge, and entation of root 
cell division takes place, the resulting cells being ee es 
small and narrow (PI. III, fig. 10; Pl. VI, fig. 31; eRe ade 
Pl. VI, fig. 44). In other words, a new growth 
starts up in the epidermis and a few of the cells of the subjacent 
layer, but principally in the epidermal cells. This stage is, of 
course, the most important for the proof of an entirely independent 
correlative origin of the coleorrhiza. 
As the root grows out from the node, the epidermal or coleor- 
rhizal cells divide by anticlinal walls, keeping pace with the root 
growth for some time, and forming the pocket or enveloping sheath 
already mentioned. 






1 Since the term “root sheath” may be applied to several sorts of 
structures, it lacks definiteness. The subject of the present account, 
however, has a distinct character, as will be demonstrated more fully be- 
low, so that it seems fitting to apply the name coleorrhiza to it. 
