Phylum Phaeophyta [ 75 



The motion of the pennate diatoms is a gliding upon surfaces, with frequent re- 

 versal, in either direction of the long axis of the cell. It depends upon the flow of a 

 stream of exposed protoplasm. This is the opinion of Max Schultze (1865), Otto 

 Miiller (1889, 1896), and Lauterborn (1896); there have been other hypotheses. 

 Miiller showed that the true raphe, without which the motion does not occur, is an 

 actual opening. The raphe is not a simple crack; it enters the wall obliquely and 

 bends at a sharp angle to come from another oblique direction to the interior. Its 

 proportions vary along its length, and it is interrupted at the middle of the valve by 

 a knob, the central granule, projecting inward from the valve. 



The pennate diatoms do not produce flagellate cells nor statospores, but they pro- 

 duce auxospores, usually by sexual processes. The majority inhabit fresh water. 



Eleven families are currently recognized. 



a. Without raphes. 



Family 1. Fragilariea [Fragilarieae] (Harvey) Kutzing Phyc. Germ. 62 (1845). 

 Family Fragilariaceae West British Freshw. Alg. 285 (1904). Cells symmetrical with 

 respect to three planes, without internal partitions. Fragilaria. Synedra. 



Family 2. Tabellariea [Tabellarieae] Kutzing op. cit. 110. Family Tahellariaceae 

 West op. cit. 281. Cells symmetrical with respect to three planes, with longitudinal 

 internal partitions. Tabellaria. 



Family 3. Bacillaria Ehrenberg Infusionsthierchen 136 (1838). Family Diato- 

 maceae West op. cit. 284. Cells symmetrical with regard to three planes, with trans- 

 verse internal partitions, solitary, or joined valve to valve in ribbons, or corner to 

 comer in zig-zag chains. Diatoma. 



Family 4. Meridiea [Meridieae] Kutzing op. cit. 61. Family Meridionaceae West 

 op. cit. 283. Cells symmetrical with regard to two planes, wedge-shaped both in valve 

 and in girdle view, with transverse internal partitions, often joined valve to valve 

 in fan-shaped colonies which are sometimes so extended as to produce spiral fila- 

 ments. Meridion. 



b. With raphes, the valves of each cell alike. 



Family 5. Naviculea [Naviculeae] Kiitzing op. cit. 90. Family Naviculaceae Rab- 

 enhorst Kryptog.-Fl. Sachsen 1: 33 (1863). This is the most numerous family of 

 diatoms. In most of the genera the cells are narrowly rectangular in girdle view, 

 narrowly elliptic in valve view, being of the shape of flat-bottomed boats. Navicula, 

 Pinnularia, etc. In other genera, as Gyrosigma and Pleurosigma, the cells are so 

 skewed as to be sigmoid in valve view. 



Family 6. Gomphonemea [Gomphonemeae] Kiitzing op. cit. 87. Family Gom- 

 phonemaceae West op. cit. 297. Cells wedge-shaped. Gomphonema. 



Family 7. Cymbellea [Cymbelleae] (Harvey) Kiitzing op. cit. 84. Family Cocco- 

 nemaceae West op. cit. 298. Cells with two planes of symmetry, in valve view crescent- 

 shaped or approximately so. Cymbella. Rhopalodia. 



Family 8. Eunotiea [Eunotieae] Kiitzing op. cit. 57. Family Eunotiaceae West op. 

 cit. 287. Cells curved as in the preceding family, the raphes reduced to brief clefts 

 near the ends of the valves. Eunotia. 



Family 9. Nitzschiacea [Nitzschiaceae] West op. cit. 301. Cells asymmetric in 

 valve view, the raphe along one margin. Nitzschia. Hantschia. 



Family 10. Surirellea [Surirelleae] Kiitzing op. cit. 70. Family Surirellaceae West 

 op. cit. 303. Each cell with two marginal raphes. Surirella. 



c. The two valves of each cell unlike, one with a raphe, one with a pseudoraphe. 



