343 



BOTANY. 



Fossil Zygophytes. — ^In the Silurian period species of Lamin- 

 wriUs, Ha/rlania, etc., probably represented the Phseosporece, which 

 order was also abundantly represented in the Devonian. Confervitea 

 occurs in the Jurassic, and in the Tertiary. Fossil diatoms of many 

 species have been found in the Tertiary; at Richmond, Va., they 

 form a vast bed nearly ten metres thick, and one at Monterey is 

 sixteen metres in thickness. 



The PELBospoREa;, containing the kelp and its allies, are marine 

 plants of an olive-brown color, varying greatly in size and structure, 

 from minute filamentous forms to the gigantic kelp with stems and 

 leaves, often a hundred metres or more in length. In previous 

 editions they were regarded as more nearly related to the Fucaceae 

 [p. 264], but their reproduction by the conjugation of similar zoo- 

 spores indicates their relationship to the zygophytic zoosporese. They 

 include the highest plants of the class. 



Twelve families, viz., Scytosiphonese, Punctariece, Desmarestiese, 

 DictyosiphoneoB, Ectocarpese, SphaoelarieiE, Leathesieee, Chordariese, 

 Asperococcese, Balfsiese, Sporochneis, Lamiuariese, are represented 

 on the New England coast by twenty-six genera and forty-eight 

 species, while many more occur on the Pacific coast, where the 

 great bladder kelp (ilfocrocj^siis ^nferas) sometimes attains a length 

 of two hundred metres or even more. 



Abrangbmbnt of the Classes and Oedees of Ztgophtta. 



a 



13 



a 



s 



a 



o 

 ft 



g 



S3 



Conjugat.*;. 



Z00SP0EE.«!. 



