STRUCTURE OF SEED. 201 



of the radicle takes some unusual development, and 

 then this kind of tubercule has been confounded with 

 several others under the name of Vitellus ; or that 

 the radicular extremity, being arrested in its elongation, 

 becomes reflected upon itself, and forms a kind of 

 perfectly close sac, which surrounds all the embryo, this 

 has received the name of Saccule, and is seen in the 

 Nymphaeaceaa. Thus, this distinction of plants into 

 Exorhizeas and Endorhizeae, which would seem to 

 promise a new confirmation of the natural division of 

 the two great classes of Phanerogamese, is found reduced 

 to a remarkable phenomenon it is true, but which 

 cannot serve for the purposes of classification. 



When at the germination of the Exorhizeae we 

 cut the extremity of the radicle at the moment it pro- 

 trudes from the seed, it is transformed, as it were, 

 artificially into an endorhizeous one ; that is to say, 

 we oblige it to produce lateral radicles, much more 

 than it was naturally intended to do. The distinction 

 of Exorhizeae and Endorhizeao, which seems so decided 

 at first sight, becomes less pronounced when we 

 examine the intermediate cases ; thus, the common 

 Radish presents below the neck two laminae applied 

 upon the root, which are kinds of Coleorhizaa, for they 

 are the remains of a kind of sheath which the radish 

 has pierced through or torn, so then we might say that 

 the Radish is an Endorhizeous plant, which shoots out 

 but one radicle. 



Radicles, whatever be their form, are often furnished 

 at the moment of their development with particular 

 hairs which are of a silvery-white colour, long, bristly, 

 but of a very soft texture, and short duration ; they 

 arise principally from near the neck, and always in the 

 parts exposed to the air ; their particular use is not yet 

 well known, but their existence is especially remarkable 



