162 



BOTANY. 



There are three orders of Brown Algae, as follows : 



Gametes alike and motile (ciliated zoospores). 



Order 7, PHiEOSPOHE^ 

 Gametes unlike and non-motile (antlierozoids and obspheres). 



Order 8, Dicttote^ 

 Antberozoids motile, the oOsplieres non-motile Order 9, FucoiDE^ 



Ordbk 7. FELSOSFOBE^. The Kelps. 



286. Kelp. — The large, flat, leaf-like kelps (Laminaria, 

 " Devil's Apron," Costaria, etc.) may be taken to illustrate 

 the larger forms (family LaminariaccB). 

 The " leaf " portion is sometimes from 

 one to six metres long and nearly a 

 metre in breadth, while its stalk some- 

 times attains a length of two to four 

 metres. It is held to rocks and stones 

 at or below low-water mark by means 

 of root-like processes. 



287. The zoospores, which have two 

 cilia, are produced in specialized cells 

 (zoosporangia) on the surface of the 

 plant (Fig. 89). These occupy definite 

 areas on the plant-body, and compose 

 the "fruit," so called. In Lami- 

 naria the zoosporangia form bands or 

 spots on the central part of the leaf. 

 The zoospores after escaping from the 

 Fig. 89. — Plant of zoosporangia swim about for a time and 



Costaria reticulata, ,, , , j- xi • j. i ^ 



allowing zoosporan- then develop directly into new plants. 



gial areas (one-sixth ,„, . „ , „ 



natural size), with sec- The union of zo spores to lorm a rest- 



tion showing zoospo- 

 rangia below, X 330. ing-spore (zygospore) has been observed 



in but few cases, and not at all in the larger and more 



common species. 



