FUCUS VESICULOSUS 97 



6. Observe the swollen tips, receptacles. Do the tips 

 of all the branches bear receptacles? How may 

 they be distinguished from the bladders? 



7. Carefully note the dot-like projections on the re- 

 ceptacles. Find the circular openings in these pro- 

 jections, the ostioles. 



8. Do you find ostioles elsewhere than on the recep- 

 tacles? If so, describe their distribution over the 

 surface of the thallus. Where are they not found? 



9. Observe carefully the emarginate tips of the 

 branches that do not bear receptacles. Do you 

 find a groove in these tips? If so, is it in the plane 

 of the thallus, or not? 



10. Make careful drawings, natural size, showing all 



points noted under C. 

 D. Microscopic Characters: 



i. Mount in water thin cross-sections taken through 

 the thin expanded portion of the thallus, and study 

 under the low power. 



Note the differentiation of the tissue into central 

 tissue or medulla, and a cortical tissue. How are 

 the two distinguished? 



3. Observe that the outer layer of cells of the cortical 

 tissue is further differentiated into an epidermoidal 

 tissue. Describe it. This outer layer is not a true 

 epidermis, like the outer layer of cells of the leaf. 

 In the younger portions of the thallus its cells, by 

 division, give rise to the cells which form the under- 

 lying tissues. None of the alga possess a true 

 epidermis. 



4. Is starch present in the cortical tissue? Chlo- 

 rophyll? Note the layer of cuticle on the outer 

 cell-walls of the epidermoidal layer. 



<. Note that the cells in the medulla tend to form a 



