The Morphology of Riippia 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 Allium 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 in the region whence the 

 root would naturally emerge. These cells become 

 filled with protoplasm, their nuclei enlarge, and 

 cell division takes place, the resulting cells being 

 small and narrow (PI. HI, fig. 10; PI. VI, fig. 31; 

 PI. VIII, 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. 



^ Since tlie term •' root slieatli " may be applied to several sorts of 

 structures, it lacks deliniteness. The subject of the present account, 

 however, has a distinct character, as wth be demonsti-ated more fully be- 

 loTv, so that it seems fitting to apply the name coleorrhiza to it. 



Figm-e 22.— Dia- 

 grammatic repres- 

 entation of root 

 arrangement ; r, 

 root ; L, leaf. 



