108 TYPE STUDIES 



T>. The molds have a method of sexual reproduction, but 

 Rhizopus nigricans only exhibits it if certain strains hap- 

 pen to be growing together, and this seems to occur rarely 

 in nature (see Blakeslee, Science, Vol. XIX, p. ^^A:, 1904 ; 

 and Proc. Amer. Acad. Arts and Science, Vol. XL, pp. 205- 

 319, 1904). Sporodinia (Sec. 107), however, readily develops 

 zygospores. Preparations may be used for this study 

 (Sec. 212). 



Questions. What is the food of the mold ? How does it 

 obtain its food ? Can solid material pass through the wall 

 of the filament ? How does it happen that Rhizopus springs 

 up so readily on bread ? Compare the structure of Rhizopus 

 with Vaucheria, noting points of similarity and difference. 



107. Sporodinia. This form grows on decaying toadstools and mushrooms 

 and frequently forms zygospores together with the sporangia. The spores 

 will grow readily on bread and other media. 



A, Study zygospores and their formation from living or preserved mate- 

 rial. Draw : 



1. A mature zygospore situated between two filaments called suspen- 

 sors. Compare their walls. Crush the zygospore and note the dense 

 contents full of oily food material. 



2. Stages in the formation of the zygospore showing (a) the union of 

 the tips of two filaments, (&) the cutting off of teiTQinal cells or 

 gametes which may be called coenogametes since they are multinu- 

 cleate, (c) the fusion of the ccBnogametes to form the zygospores. 



B. The sporangia of Sporodinia make an interesting study in comparison 

 with those of Rhizopus. 



108. Saprolegnia or Achlya, water molds. Place a dead fly, or a pellet of 

 meat, or bits of bread in a dish containing pond or ditch water. After two 

 or three days note the gradual development of a halo of radiating hyphse. 

 Make a habit sketch of the growth upon the substratum. 



A. When some of the ends of the hyphse become swollen and white cut 

 out a portion of the mycelium with the scissore and mount in water. 

 Study the hyphae. "What is their structure compared with that of 

 the molds ? Draw a tip showing arrangement and character of the 

 protoplasm. 



B. Examine the swollen tips, some of which should be sporangia with 

 zoospores in various stages of development. Draw under h.p. : 



1. A mature sporangium full of zoospores. 



2. Stages in the development of sporangia. 



