NUTRITION. 41 



term rhizoma is then applied to them ; and 

 sometimes they are much swollen, and called a 

 tuber; or if they (or rather their leaf buds) (35) 

 thicken below the ground, a corm. All these 

 forms of stem have been called roots ; but there 

 are two marked distinctions between these and 

 true roots. They have what are termed nodes, 

 which are the points at which the leaf buds are 

 formed, as well as leaf buds, which are never 

 found on roots properly so called. Scales being 

 the rudiments of leaves, no proper root can be 

 scaly. 



32. The stems of Endogenous plants, consi- 

 dered generally, have as their common charac- 

 ters. 



1. They are composed of one single homo- 

 geneous mass. 



2. They have no true medullary channel 

 nor distinct medullary rays. 



3. Their older fibres are on the circumfe- 

 rence, and the newer deposits in the centre, 

 from which latter circumstance they take their 

 name. 



They are less marked in character, and pre- 

 sent less regularity of structure than the Exo- 

 genes. Tims one species, the Palm, will afford 

 a sufficient idea of the whole class. This stem 



