56 



ORGANOGRAPHY. 



BOOK I. 



of annual duration from the surface of the earth are called 

 herbs. 



Some botanists distinguish two sorts of stems, the characters 

 of which are derived from their mode of growth. When a 

 stem is never terminated by a flower-bud, nor has its growth 

 stopped by any other organic cause, as in Veronica arvensis, 

 and all perennial and arborescent plants, it is said to be in- 

 determinate ; but when a stem has its growth uniformly 

 stopped at a particular period of its existence by the production 

 of a terminal bud, or by some such cause, it called determi- 

 nate. The capitate and verticillate species of Mint owe their 

 differences to causes of this nature ; the stem of the formei 

 being determinate, the latter indeterminate. 



The point whence two branches diverge is called the «xi4 

 or, in old botanical language, tlie ala. 



Leaf-buds {Gemma, Linn.; Bourgeon, Fr.), being the rudi- 

 ments of young branches, are of great importance in regard 

 to the general structure of a plant. They consist of scales 



16. 



17 



imbricated over each other, the outermost being the hardest 

 and thickest, and surrounding a minute cellular axis, or grow- 

 ing point, which is in direct communication with the woody 

 and cellular tissue of the stem. In other words, they may be 

 said to be growing points covered with rudimentary leaves for 

 their protection, and to consist of a highly excitable mass of 

 cellular substance originating in the pith, and having a special 

 power of extension in length. Under ordinary circmnstances, 



