66 ELEMENTARY BIOLOGY. [CHAP. 



6. [Cut off half an inch of the growing end of the stem, 

 imbed it in paraffin upside down, and cut a series of 

 transverse sections : examine them with the microscope, 

 beginning with those farthest from the growing point. 

 At first the various tissues described in 3 and 4 will be 

 readily recognisable; as the sections nearer the grow- 

 ing point are examined they will be less distinct, and 

 close to the growing point the whole section will be 

 found to be composed entirely of parenchymatous 

 closely-fitting cells.] 



[c. The leaf. Imbed a leaf in paraffin and cut a thin 

 vertical section : examine with I inch obj. It will be 

 found to be constructed essentially on the same plan 

 as the leaf of the bean. (VIII.)] 



d. The reproductive organs. 



1. Examine a sorus with a low power without a cover- 

 glass. It is composed of a great number of minute 

 oval bodies, the sporangia. 



2. Scrape off some sporangia and mount in water: ex- 

 amine with i inch obj. 



a. Their form: they are oval biconvex bodies 

 borne on a short stalk. 



b. Their structure: composed of brownish cells, one 

 row of which has very thick walls, and forms a 

 marked ring (cumulus'] round the edge of the 

 sporange. 



c. Their mode of dehisccnce (look out for one that 

 has opened): by a cleft running towards the 

 centre of the sporange from a point where the 

 annulus has torn across. 



3. Burst open some sporangia by pressing on the cover- 

 glass: examine, with \ obj., the spores which are set 

 free. 



