32 COMPOUND OKOANS OF PLANTS. 



in the earth as in the atmosphere in p, form beautifully appro- 

 priate to the altered condition of the medium. 



CHAPTER III. 



ON THE ROOT OR SUBTERRANEAN APPENDAGES OF THE 

 AXOPHYTE. 



The rhizoma or the subterranean part of the vegetable axis, 

 has appendages like the aerial part, organically adapted to the 

 medium in which they are developed. These appendages, 

 emitted by the rhizome or its ramifications, are ordinarily 

 under the form of fibres more or less slender and delicate, 

 commonly cylindrical, simple or branched, called radicle fibres. 

 It is the assemblage of these fibres which constitute the true 

 root, that is to say, the organ whose function is to draw from 

 the soil a part of the elements necessary to the life and 

 development of the plant. 



Each of these fibres is terminated by a blunt and rounded 

 extremity, which has received the name of spongiole. For a 

 long time this was considered to be the only part of the root 

 which absorbed liquids. But it is now ascertained that absorp- 

 tion takes place throughout the whole extent of the radicle 

 fibres, the centre of which is occupied by bundles of vessels. 



The spongioles or spongelets ought not to be reckoned special 

 organs. Fig. 8 is the extremity of the young root of the 

 sugar maple, (Acer saooharinum,) highly magnified. Now the 

 cellular extremity of the root or the spongiole, a, does not con- 

 sist of the cells most recently formed, which are in reality an 



