312 CALIFORNIA ACADEMY OF SCIENCES. IProc. 3D Skr. 



wall, and such embryos resemble very much the embryo of 

 such grasses as Triticum and Hordeum, figured by Norner 

 (1881). Hegelmaier does not show these oblique walls in 

 his figures of S. ramosiim, and in this respect S . simplex is 

 more like the grasses than is S. ramosiim. 



The primary tissues are now pretty well defined. The 

 central plerome-strand extends to the basal wall and is sep- 

 arated from the epidermis by one layer of periblem cells 

 (fig. 46). In the segment below, the superficial cells, as 

 we have seen, divide again by periclinal walls, so that there 

 are often two well defined layers of cells, evidently derived 

 from a periclinal division of the primary epidermis. In the 

 basal segment there are seldom more than four cells, and 

 in case there is another segment between the basal one 

 and the second segment (fig. 51) its divisions are quite 

 irregular. 



Hegelmaier's account of the origin of the different mem- 

 bers of the embryo in S. ramosum corresponds closely to 

 what was seen in S. simplex. Much the greater part of the 

 embryo is taken up by the cotyledon which elongates rap- 

 idly, so that the embryo soon becomes several times longer 

 than broad, this growth in length being mainly in the coty- 

 ledon, the stem and root remaining short. The stem-apex 

 originates from the terminal segment, but on one side well 

 toward the base. Its position and origin correspond closely 

 to those in the grass-embryo, to judge from Norner's 

 account and figures (Norner, 1881). In its origin from 

 the terminal segment it differs from such Monocotyledons as 

 Alisma and Naias, where the stem-apex belongs to the sec- 

 ond segment. Zannichellia, however, has a terminal stem- 

 apex, and Solms-Laubach (1878) describes several Mono- 

 cotyledons with terminal stem-apices. In Lilcea (Campbell, 

 1898) the stem-apex is probably derived from the terminal 

 segment as in Sparganium. Sparganium is, therefore, in 

 regard to the origin of the stem-apex, intermediate between 

 such extreme forms as Zannichellia and the majority of 

 Monocotyledons investigated, in which the stem-apex arises 

 from the second segment. 



