90 TYPE STUDIES 



1. That the zoospores are developed in varying numbers in 

 the cells. Make counts and draw the various conditions. 

 Certain striking peculiarities of the zoospores, the pig^ 

 ment spots (See 3), are easily recognized at this time. 



2. The escape of the zoospores from the parent cells, 

 sporangia, and their swarming movement in the water. 

 They are sometimes called swarm spores. 



3. The structure of the zoospore, showing pigment spot, 

 chromatophore, number and position of the cilia, gener- 

 ally four in number and made clear when material is 

 stained with iodine as described in Sec. 67, B. Which is 

 the forward end of the zoospore ? Draw. 



4. Should two-ciliate motile cells be present, they may be 

 expected to unite, or conjugate, in pairs in the water, 

 showing that they are sexual cells, or gametes. The prod- 

 ucts of the fusion are four-eiliate cells with two pigment 

 spots. These are zygospores, or zygotes. 



Because the form or morphology of these gametes is similar, 

 this type of sexual reproduction is called isogamy. 



E. Note that the zoospores gather on the illuminated side of 

 the vessel and settle down to germinate. After the material 

 has been in the vessel for three or four days, observe the 

 growth of young plants, or sporelings. Gather some of the 

 sporelings with a pipette and draw a number of stages illus- 

 trating the germination of the zoospore. Observe the older 

 sporelings, taking on the appearance of the parent plants, and 

 the development from the basal cell of a holdfaM, 



Eefbeencb. Principles, Sec. 217. 



Questions. Describe as fiiUy as possible the life history of 

 Ulothrix or whatever other form may be studied. What 

 organisms do the zoospores resemble ? In what particulars ? 

 Of the two periods in the life history, the motile and quies- 

 cent, which represents the more primitive condition of 

 plant life ? Which is now the more important for vegeta- 

 tive activities ? Which for reproductive ? 



