124 TYPE STUJ)TES 



B. VegetatAve structure. 



1. Mount some of the leaves in water. Note the simple cell structure. 

 Are these leaf -like scales related, that is, homologous, to the leaves 

 of ferns and seed plants ? Draw a portion of the leaf and show 

 details of cell structure, arrangement of chloroplasts, etc. 



2. Examine the rhizoids, if found, and compare with those of Mar- 

 chantia. Draw. 



3. Lengthwise microtome sections of the growing points will show the 

 method of growth from an apical cell and the development of the 

 leaves. 



C. The antheridia, or male sexual organs. These are found in Porella on 

 small special branches at the side of the stem near the tip of the plant. 

 Draw an antheridial branch or group of branches. 



1. Tease the leaves of an antheridial branch apart, under a dissecting 

 microscope if possible, and find the antheridia. How are they borne 

 with reference to the stem and leaves ? Show their position in a 

 diagram, 



2. Draw an antheridium, noting the long stalk and the sperm case. 

 Crush older antheridia and observe the contents with developing 

 sperms; stain with iodine. 



3. Lengthwise microtome sections of the antheridiaLbranches (Sec. 212) 

 show clearly the cell structure of the antheridia and their develop- 

 ment, and also the development of the sperms. 



D. The archegonia, or female sexual organs. Search plants, not bearing 

 antheridia, for short lateral branches in which the rather large leaves 

 form close tufts. These are archegonial branches. The sexual organs 

 of Porella are therefore on separate plants, male and female, and the 

 genus is therefore dioecious. 



1. Dissect these branches carefully and note a sac-like envelope (peri- 

 anth) around a terminal group of archegonla. Diagram their position. 



2. Tease the archegonia free from the surrounding leaves and envelope 

 and draw one or more. Note their form in comparison with the 

 archegonia of Marchantia. 



3. It will frequently be found that one of the archegonia has been 

 fertilized and that a young sporophyte is present in its much en- 

 larged base, now called the calyptra. 



E. The sporophyte. Old sporophytes, also called fruits, may be found at 

 the tips of old archegonial branches. Dissect away the leaves and 

 envelope around the base. Note : 



1. The relatively long stalk attached to the tip of the sexual plant 

 (gametophyte) by ?(,foot. 



2. The terminal spore case generally split lengthwise into four parts. 



