28 



FAMILIAR LESSONS IX BOTANY. 



63. You liave now learned that leaves spring at regular 

 intervals along the branches, and that these points are 

 called nodes; that their different manner of folding them- 

 selves in the bud is called their vernation. You see from 



Fig. 14. 



this cut that the leaf is divided into three parts: a is the 

 petiole or leaf stalk, 5 the midvein, and c the lamina. The 

 petiole, if you will observe, seems to run through the en- 

 tire length of the leaf, and is called the midrib. It sup- 

 ports the leaf, and from it the veins which form the netted 

 framework of the leaf springs. Those veins which spring 

 from the midvein are called primary, those branching from 

 the primary are called secondary, and the smallest are 

 veinlets. The midrib is never wanting, though the petiole 

 is. I have before told you that a leaf destitute of a petiole 

 was said to be sessile.* 



• Prof. McCosh, some years ago, presented to the British Association for tJie Advancement 

 of Science a paper npim the venation of exogenous plants, in which he asserts that the leaf is 

 the type of the whole ph»nt, that the distribution of the branches along the axis and the distri- 



G3. What have yon now learned ? What does the cnt represent ? How many- 

 parts has a leaf ? What are they? How does the petiole run ? What is it called ? 

 Veins springing from the midrib are called what ? Have all leaves a midrib ? 

 Have all a petiole ? When the petiole is absent, what is the leaf said to be ? 



