THE ROOTS OF PLANTS. 159 



arrangement of lateral members as given in Hofmeister's "General 

 Morphology." * 



(e) Tlie internal structure of the leaf may be easily studied. The 

 most important sections are those made at right angles to the surface ; 

 but some should be made alt-o parallel to it, so as to show the form of 

 the palisade cells and the dispositions of the cells in the loose tissue of 

 the under surface. The leaves of the lilac, apple, cherry, Tmpatiens, 

 Sttphium, sunflower, etc., are very good for this study. The more 

 difficult sections can be more easily made after soaking the leaves for 

 some time in strong alcohol, thus hardening them. 



VI. OF THE BOOTS OF PLANTS. 



205. The root differs from all other members of the 

 plant in being tipped with a peculiar mass of cells the Root- 

 cap (pileorhiza f) and in originating cndogenously ; from 

 stems it differs in never producing leaves or other phyllome 

 structures. There is some doubt as to whether the Primary 

 Root i.e., the first root of the embryo is not in many cases 

 formed otherwise than endogenously ; J but all common roots 

 certainly are developed from beneath the surface of other 

 parts of the plant. 



206. Roots may develop from any part of a plant which 

 contains fibro-vascular bundles, so that it is no uncommon 

 thing for them to issue from stems (particularly their nodes) 

 and leaves, as well as from other roots. Whatever their 

 origin, they are essentially alike, the differences, as before 

 intimated, being of minor importance. They all agree in hav- 



itself, so that the two sides exposed to the air and light are said to be 

 in reality the under surface. A study of the very young leaf of the 

 Iris, along with that of Hemerocallis, shows them to be alike ; both are 

 composed of an upper laterally flattened portion and a lower channelled 

 one ; in the Iris the upper portion grows fully as much as the lower, 

 while in Heinerocallis the growth is almost entirely confined to the lower 

 portion, the upper extending but little and forming the small extremity 

 of the leaf. The small tip of the leaf in the latter case is clearly the 

 homologue of the whole of the so-called ensiform leaf of the former. 



* " Allgemeine Morphologic der Gewachse," von Wilhelm Hofmeis- 

 ter ; Leipsig, 1868. 



f From the Greek m'AeoS, a cap, and frifa, a root. 



| The mode of formation of the Primary Root will be taken up for each 

 group of plants in Part II. 



