EXEECISES. 205 



each other ; they are deciduous, or withering and falling ; 

 or persistent, remaining ; they areJlabeUiform, or fan-shaped ; 

 or imbricated, placed one over another, like the tiles of a 

 house. They are also succulent, soft and juicy, coriaceous, 

 resembling leather, &c., &c. ; the areolcs are the spaces from 

 which the leaves have fallen. 



Venation constitutes a highly important character in fossil 

 botany, since the veins often afford very conclusive evidence 

 as to the generic character of a plant. The costa is the mid- 

 rib from which the smaller veins usually proceed ; these are 

 simple, (that is, undivided,) or dichotomous, (forked,) once, 

 or more than once ; anastomosing (running into each other) ; 

 reticulated, forming a net-work; or radiating, proceeding 

 from a centre, like the spokes of a wheel, &c., &c. See 

 Dr. Lindley, Sir J. E. Smith, Sir W. Hooker, &c., &c. 



EXEECISES. 



Otf FOSSIL BOTANY. 



1. Describe the arrangement of plants according to the 

 natural system of Jussieu. 



2. Explain the term, cotyledon. 



3. Describe the monocotyledonous and dicotyledonous 

 divisions of plants. 



4. Show the difference of the two classes, as developed in 

 the seed, the wood, and the leaf. 



5. Describe the successive epochs in the Elora of the 

 ancient earth, as proposed by Brongniart, and modified by 

 Sternberg. 



6. Name the six divisions of the vegetable kingdom 

 adopted by Brongniart. 



7. Copy and commit to memory the eighteen families 

 which form the six divisions above stated. 



8. State the experiment of Dr. Lindley, as to the power 

 of certain plants to resist decomposition in water, and its 

 results, with the remarks of Count Sternberg. 



