HOW TO KNOW THE SEAWEEDS 



8a Growing apices showing a single apical cell, although this some- 

 times sunken in an apical pit {Chondria, Laurencia) or obscured 

 by terminal branchlets (especially Dasya. Digenia, Wrangelia) Fig. 

 18 26 



Fig. 18. Examples of apical cells. 



A. As found on an acute apex. B. As 

 found on a blunt apex such as Gelidium 

 (seen in longitudinal section). C. Sunken 

 in an apical pit as in Laurencia. D. Some- 

 what obscured by terminal branchlets (or 

 trichoblasts or hairs) as in Polysiphonia. 



In making observations of apical cells 

 one will usually have the best results 

 with young, actively growing vegetative 

 branch-tips rather than old or fertile ones. 

 In those plants in which the apex is ob- 

 scured by enveloping branchlets it may 

 be necessary to dissect away the very 

 tip of a yoimg branch and to crush it 

 under the cover slip on a sHde in order to force the surrounding branch- 

 lets away and to make the apical cell area visible. 



Figure 18 



8b. Growing apices without a single apical cell from which growth 

 takes place 9 



9a Growth trichothallic. Fig. 19 24 



Fig. 19. An example of trichothalUc growth 

 by means of a terminal hair with cell di- 

 vision at its base, as seen in the apex of 

 Haplogloia andersonii, X 300. Note that 

 the trichothalUc type of growth will be dif- 

 ficult to interpret in Heterochordana abieti- 

 na (See Fig. 42). Its distinctive habit should 

 be recognized. 



Figure 19 



31 



