ECTOCAKPUS 97 



cells to the shields is difficult to determine, and is best omitted in a 

 general study. 



C. Crush old oogonia containing thick-walled oospores and note the cell 

 contents full of food material. Test its nature with iodine. 



D. Should the material be a species free from lime (especially in the case 

 of Nitella) and one whose internodal cell is not covered by corticating 

 filaments, study the circulation of protoplasm in the internodal cell as 

 described in Sec. 64, B. 



B. A detailed histological examination of a stonewort is full of interest, 

 but rather special for a general course. Its full understanding demands 

 a study of microtome sections of the growing points, to establish the 

 remarkable method of growth, which can be followed throughout the 

 branchlets and corticating filaments that grow over the internodes 

 in many species. The method of growth furnishes the key to the 

 detailed morphology of the stoneworts. 



Reference. Goebel, 16, p. 52. 



THE BEOWN ALG^, OR PHiEOPHYCE^ 



92. Field work on the marine algae. Study when possible the distribution 

 of marine algse on rocks at the seaside. Describe the conspicuous growths 

 in three zones : (1) those well above low-tide mark ; (2) those at low-tide mark ; 

 and (3) those below low-tide mark. Where are the sea lettuces most numer- 

 ous ? the rockweeds 1 the kelps ? the larger red algse ? Examine sunlit tide 

 pools and compare with very shaded pools. If sheltered bays can be studied, 

 note the character of the forms on stones in shallow water, and on the eelgrass. 

 If salt marshes can be examined, study the algal flora along the margins of 

 the tidal streams and in the pools. Make collections of the conspicuous 

 forms, noting their habitats, and bring to the laboratory for examination. 



93. Ectocarpus. Examine the habit of the plant, tufted growth, attach- 

 ment. 



A. Draw a portion under m.p. to show the branching. Are the tips of 

 the filaments all alike in structure ? Tiy to determine the method of 

 growth when they end in hairs. Draw a cell under h.p., showing the 

 irregular chromatophore. 



B. In fruiting material find either or both of the two forms of sporangia. 

 Draw under h.p : 



1. Unilocular sporangia, single cells, solitary, sessile, or on short stalks 

 in some species and in chains in others, as in Pylaiella (Ectocarpus) 

 littoralis. Each sporangium develops a large number of two-ciliate 

 zoospores. 



