292 THE BIOLOGY OF THE PLANT 



vides to form the surrounding tissues? Trace 

 back into the older portions of the branch the 

 rows of cells which have their origin from the 

 initial cells. How do these tissue-cells change in 

 shape and contents as they get older ? 



Draw your section. 



Make transverse sections across the young branch, 

 cutting through the growing point as well as above 

 and below it. 



Compare with the longitudinal section and draw. 



c. The vesicles. — Examine transverse and longitudi- 



nal sections of the walls of the vesicles. Do you 

 find all of the tissues present ? Look for vesicles 

 in various stages of development. Judging from 

 their structure, how do you imagine the vesicles to 

 be formed ? Draw the sections. 



d. The conceptacles. 



1. The sterile conceptacles. — With a hand-lens 

 search among your sections for some which 

 have passed through the conceptacles. Mount 

 several of these sections in a drop of the mixt- 

 ure of glycerine and acetic acid, examine with 

 the low power, and find a section which has 

 passed through the centre of a conceptacle. 

 What is the shape of the cavity? How is it 

 formed? Is the cavity apparently anything 

 more than a depression of the surface of the 

 thallus ? How much of the width of the section 

 (thickness of the thallus) does a conceptacle 

 occupy? Notice the cluster of hairs or tri- 

 chomes in the conceptacle. What is their rela- 

 tion to the opening or ostiole of the concep- 

 tacle ? What part of the conceptacle forms the 



