PORELLA 123 



3. INIicrotonie sections of (he sporopliytes (Sec. 212) arc necessary for 

 a study of the details of deveU)pment and spoi'e formation and the 

 relation of the foot to the tissue at the base of the archegonium. 



Reference. Campbell, 23. 



Questions. What are the advantages in the form and position 

 of the thallus of Marchantia ? What are its life habits ? 

 What are probably its most effective means of multiplica- 

 tion ? What great advance in structure is presented by the 

 sexual organs over those of the algse generally ? Under 

 what conditions are the sperms set free and the eggs ferti- 

 lized ? W^hat new features are introduced by the develop- 

 ment of the Q^g after fertilization, — features not generally 

 present in the algie? Are there spores among the alga^ 

 comparable to the spores of Marchantia ? Is it a new type 

 of spore in plant evolution ? Describe the life history and 

 distinguish between the sexual phase, or gametophyte, and 

 the asexual phase, or sporophyte. What is the physiological 

 relation of the sporophyte to the gametophyte ? Draw and 

 arrange a series of diagrams illustrating the chief stages 

 throughout the life history, using two colored pencils to 

 designate gametophytic and sporophytic phases respectively 

 (App. 18). Construct a life-history formula which will ex- 

 press this succession (App. 18). 



125. Porella, a leafy liverwort. Frullania, Eadula, or other types may also 

 be studied by a similar outline. Examine living material and describe the 

 life habits. Note the dying away of older parts of the plants. 



A. General morphology. Study and compare the two surfaces of the 

 plants. 



1. Draw the upper surface. Note the stem bearing two rows of over- 

 lapping leaf-like scales, generally called leaves, at the side. Is the 

 branching regular? Observe the bud-like structure of the gruiu- 

 ing point. 



2. Draw the lower surface. Note the third row of small scales or 

 leaves (amphigastria) somewhat irregularly distributed along the 

 stem ; also show the under side of the lateral rows. Searcii for 

 rhizoids. 



