208 



Methods in Plant Histology 



for illustrative purposes. It floats freely on the surface of ponds and 

 ditches. Early in the spring (during April in the Chicago region) it 

 produces antheridia; then, for a short time (about the first of May) 

 both antheridia and archegonia, and still later only archegonia. 

 Sporophytes then appear as black dots along the grooves. After the 

 spores are shed, the thallus remains sterile for the rest of the season. 

 Marchantia and similar forms are not difficult to establish out of 

 doors. A rather damp, shady spot close to the north side of a build- 

 ing is best. Scrapings from a board which has been nearly burned 

 up makes the best fertilizer to scatter on the soil, if one is to cultivate 

 Marchantia. Such freezing as Marchantia receives in the vicinity 



of Chicago does not pre- 

 vent it from appearing 

 again the next spring. 

 If it is desirable to have 

 material throughout the 

 year, the out-of-door 

 culture may be made 

 in a box which can be 

 brought into the labora- 



A 



B 



FIG. 60. Ptilidium ciliare: A, longitudinal, and B, 

 transverse section of the apical region of the leafy 



gametophyte. X420. tory or greenhouse in 



the winter. A box 3 



feet long, 2 feet wide, and 1 foot deep will be convenient. It should 

 have a glass cover; an old window will do. There should be about 

 six inches of dirt in the box. A mixture of sand, loam, and charred 

 scrapings will make a good substratum for Marchantia. If one is to 

 raise liverworts in the laboratory, it is absolutely necessary to note 

 carefully the conditions under which they grow in the field. 



The living plants are very desirable, since they not only furnish 

 the best possible material for habit work and the coarser microscopic 

 study, but they also enable one to secure complete series in the 

 development of the various organs. 



The Thallus. In many cases it will not be necessary to make a 

 special preparation for the study of the thallus, since preparations of 

 antheridia, archegonia, or sporophytes may include good sections of 

 vegetative portions. This is particularly true of forms like Riccia, 



