142 TYPE STUDIES 



division differentiate four regions, which develop respectively 

 into stem, root, first leaf, and a large foot. These stages can 

 only be studied from microtome sections. The first leaf 

 and root grow rapidly and in a few days break through the 

 much-enlarged archegonium (calyptra). 



1. Watch the development of the sporophytes in a culture 

 of spores. When about one week old draw a megaspore 

 with the attached sporophyte imder l.p. Determine by the 

 root cap which portion is root and which leaf. The stem 

 lies at the base of the leaf. Where is the foot ? 



2. Crush the megaspore and observe the condition of its 

 food contents. What has furnished the food for the 

 development of the sporophyte ? 



Reference. Campbell, 23. 



Questions. What are the growth habits of MarsUia ? What 

 are the life conditions governing the germination of the 

 spores and development of the gametophytes ? What is 

 heterospory ? What are the advantages in the differentia- 

 tion of a large megaspore richly supplied with food ? What 

 are its advantages in giving the sporophyte a better start 

 in life ? Describe the life history, distinguishing between 

 the sexual phases, male and female gametophytes, and the 

 asexual phase, sporophyte. Draw and arrange a series of 

 diagrams illustrating the chief stages throughout the life 

 history, using two colored pencils to designate the gameto- 

 phyte and sporophyte generations respectively (App. 18). 

 Construct a life-history formula that will express this 

 succession (App. 18). 



THE HORSETAILS, OR EQUISETINE^ 



133. Equisetum arvense, the field horsetail. This is the com- 

 monest of the horsetails and is abundant along railroad tracks, 

 roadsides, river banks, and bare northerly slopes. The sjjore- 

 bearing shoots appear early in April and are followed shortly by 



