50 CAL/FOAW/A ACADEMY OF SCIEiVCES. [Proc. 3D Ser. 



VII. The Cotyledon. 



The cotyledon is formed from one of the two cells into 

 which the terminal segment is first divided. If the primary 

 division is oblique it is the larger of the two cells which 

 forms the cotyledon. In any case the latter grows more 

 rapidly than the stem-apex, and is soon evident as a protu- 

 berance on one side of the apex (fig. 118), which continues 

 to increase in size until it assumes a distinctly conical form. 

 Its subsequent growth is very much like that of JVaias, the 

 main difference being the less completely developed sheath 

 at the base and the characteristic elongated and outwardly 

 curved apex (fig. 124). Owing to the slighter development 

 of the stipular sheath, the cavity thus formed and surround- 

 ding the stem-apex, is not completely closed in front. 



VIII. The Stem. 



The young stem-apex (fig. 118, 5/) is covered with a well 

 defined epidermis, continuous with the rest of the embryo, 

 and beneath this is a single layer of periblem cells, separat- 

 ing the epidermis from the plerome, which is connected 

 directly with that of the cotyledon and root. As the embryo 

 enlarges the stem-apex becomes more prominent and forms 

 a projecting almost hemispherical prominence within a well 

 marked cavity formed by the encircling base of the cotyle- 

 don (fig. 120). From It is formed later the second leaf 

 (fig. 121, P). This arises as a protuberance upon the side 

 of the stem-apex, opposite the cotyledon. Its tissues are 

 continuous with those of the stem and show the same rela- 

 tive arrangement. 



IX. The Root. 



As might be expected from the larger part of the young 

 embryo which takes part in its formation, the primary root 

 in ZannicheUia is relatively larger than in JVaias. The 

 greater part of the root is formed from the second and third 

 of the primary segments of the embryo, and in consequence is 

 longer than that of the same stage in Naias. These segments 



