102 TYPE STUDIES 



C. The male or antheridial plant. 



1. Sketch in outline tlie position of the male organs, or antheridia, in 

 clusters at the tips of the filaments. 



2. Draw the outline of an antheridium on a large scale and fill in the 

 details of a portion showing the outer layer of small, colorless cells 

 which develop the sperms. 



3. Crush an antheridium and try to determine its general plan of struc- 

 ture. There is a central siphon surrounded by a densely branching 

 system of small cells ending in the sperms at the periphery. Diagram 

 the relation of these parts. Trace the development of the antherid- 

 ium. It should be clear that the organ is a modified branch. 



D. The female or cystocarpic plant. 



1. The fructification, called a cystocarp, is in Polysiphonia an urn- 

 shaped structure in which a cluster of carpospores is developed from 

 a large cell at the base. Draw a mature cystocarp and afterwards 

 crush out the pear-shaped carpospores. 



2. Examine younger cystocarps, tracing the structures back to the 

 female organ, or procarp. The procarp is a modified branch and 

 many celled. The carpogonium is enveloped by sterile cells, from 

 among which the trichogyne projects somewhat at one side. 



The development of the cystocarp is too difficult a subject for general 

 study. It has recently been traced by Yamanouchi {Botanical Gazette, 

 Vol. XLII, p. 401, 1906), who has established an alternation of 

 tetrasporic plants with the sexual. The former, together with certain 

 developments from the carpogonium leading to the production of the 

 carpospores, constitute an asexual or sporophytic phase in the life 

 history. The sexual plants- are gametophytes and the sporophyte 

 generation begins with the fertilized carpogonium and ends with 

 the formation of the tetraspores, thus including the spore-produc- 

 ing tissues of the cystocarp, together with the tetrasporic plant (see 

 Principles, Sees. 245, 246). 



THE BACTEEIA, OE SCHIZOMYCETES 



100. The culture of bacteria on potato** (App. 14). 

 A. Preparation of the culture surface. 



1. Select medium-sized, sound potatoes, and boil with the 

 skins on for fifteen minutes, — not so long that they 

 will not readily hold their form when cut. 



2. While the potatoes are cooking, boil six Petri dishes in 

 clear water for fifteen minutes. Lift the Petri dishes out 



