A MANUAL OF BOTANY 133 



lower opidormis, and third, tlio. iiiiddhi mass of cells (ineso- 

 ph}' 11). What shape have the cells ? Where is the chloro- 

 phyll located ? The mesophyll cells are filled with living 

 protoplasm, hence are the active working cells. Observe 

 that the stomates open into irret^nilar dir chdinbers. What 

 structures are found in these chandlers ? What color have 

 they ? Observe the rhizoids projecting from the lower sur- 

 face, or study them separately and find the variations in 

 form. If no fresh section is available, study a figure in 

 some reference book. 



Sexual reproduction. On certain tlialli observe two kinds 

 of erect stalks, expansed at the summit, the fruiting or re- 

 productive branches bearing the gamete bodies. How do 

 these two forms differ ? The one with the divided toj) or 

 receptacle is the archegonkil branch. The other is the axther- 

 idial branch. What shape has its receptacle ? Are both 

 kinds on the same thallus or not ? Study })rei)ared sections 

 of each receptacle, or figures of the same in your reference 

 books, and observe the archegonia depending below and the 

 antheridia in the upper surface of the respective receptacles. 

 When mature, the sperm and the archegonial oosphere of 

 these plants unite to produce a spore, which grows into a 

 flask-shaped structure, which you can see on the mature re- 

 ceptacle of the archegonial branch, hanging downward {the 

 sporopluite). The sporophyte, when mature, contains many 

 spores, mixed with the elastic filaments of peculiar nature, 

 elaters, which assist in scattering the spores. These on ger- 

 mination produce the thallus forms studied at first. 



Conclusions. What reason can you give, or find in refer- 

 ence books, for the two methods of reproduction '.' How do 

 these plants get into the greenhouses? What difYorences 

 are there between the spores and gemmae ? Exi)lain the 

 placing of the liverworts with the true mosses in the moss- 

 plant branch ? What new structural features are seen in 

 the liverworts for the first time ? What is meant by the 



