84 LABORATORY AND FIELD EXERCISES 



shown in the section ? Is Fucus composed of a true 

 cellular tissue like a geranium ? Make an outline 

 drawing of the section, shading in the chlorophyll- 

 bearing layer. Detail a few cells of each layer to 

 show the cellular structure. 

 3. Reproduction. 



a. Reproductive branches. Eead the text description of 



reproduction in Fucus. 



(1) How are the reproductive branches distinguishable 



from the ordinary vegetative branch tips ? Find 

 the male reproductive branches, covered with a 

 yellow exudation of slime containing the male 

 gametes. Learn to recognize the female branches 

 by the greenish exudation of slime containing 

 female gametangia. 



(2) Ostia, or pores. Observe ostia with a hand lens on 



the surface of the reproductive branches or with 

 a low power in thin horizontal surface sections of 

 reproductive branches. 



b. Crametes and gametangia (living material). 



(1) Male gametangia and gametes. Touch the surface 



of a slide with male branches which are exuding 

 yellow slime. Mount and observe the saclike 

 male gametangia containing male gametes, which 

 look like yellow dots. Look for male gametes 

 free from the gametangia on the slide. Can you 

 distinguish the movement of these male gametes ? 

 their form and structure ? A brick-red spot, " the 

 eyespot," is usually visible. 



(2) Draw male gametangia and gametes somewhat 



magnified. 



(3) Female gametangia and gametes. These may be 



obtained as in the case of the male gametes. Note 



