2\2 VEGETABLE ORGANOGRAPHY. 



1st. The greatest number of plants present the coty- 

 ledons absolutely flat, that is to say, without any curve 

 or folding ; such are those of Cytisus, Ricinus, Arabis, 

 &c. ; this form is compatible with every position of the 

 radicle. 



2d. There are some which are folded longitudinally 

 upon their middle nerve ; these always have the radicle 

 dorsal ; such are, for example, the Cruciferse Ortho- 

 ploceaa ; these cotyledons are said to be Conduplicate, 

 and are designated by the sign o^. 



3d. There are some curved or rolled spirally, in a 

 longitudinal direction, as, for example, those of the 

 Combretaceae — Puyiica, Helicteres, &c. 



4th. Some are bent double, as in the Cruciferae Di- 

 plicolobiae, such as Heliophila. 



5th. We find cotyledons flat, but rolled crossways one 

 upon the other, as, for example, in the Cruciferae Spiro- 

 lobeae, such as Bunias. 



6th. Lastly, there are some which are irregularly 

 plaited or crumpled upon one another ; such are those 

 of the Mullow. 



This kind of character does not appear connected in 

 an intimate manner with the symmetry of plants, since 

 there are families where we find united several of these 

 different foldings of the cotyledons ; the Cruciferaa, in 

 particular, present five different systems. 



As leaves, some cotyledons are furnished with petioles, 

 others are sessile ; the former, as well as several of the 

 latter are, as it were, articulated at the base, and fall off 

 soon after germination ; there are, however, annual 

 plants, where they remain until the flowering, as some 

 species of Veronica and Galium, &c. Sheathing coty- 

 ledons, or even simply sessile ones, are more permanent, 

 or only destroyed in part. Those of several succulent 

 plants are particularly remarkable for their permanence; 



