22 



THE STRUCTURE AND LIFE 



" I have never seen," writes this skilled observer (') " the gelatinous 

 matter produced, nor the protoplasm form the spore any more than I have 

 seen the protoplasm escape naked from the valves ; on the contrary I have 

 always seen the protoplasm surrounded by an extremely thick and resisting 

 membrane." In the following words he sums up in all its simplicity 

 the phenomenon of the re-establishment of the form of diatoms as 



follows : 



" The contents of the microfriistule hardens, and is surrounded by a strong 

 membrane ; then without other visible phenomena this quasi-spore germinates 

 and produces what is nothing less than the diatom of re-established form." 



Professor H. L. Smith has on his part observed the return to the 

 sporohgial form in Cymbella euspidata, and describes and figures it ( 2 ) exactly 

 as Dr. Miquel has done Nitzschia palea. 



2. Two different frustules approach one another and pour out their 



cellular contents ; from this mixture is borne a 

 single sporonge, which gives rise to the production 

 of a sporongial frustule. 



Professor H. L. Smith has personally obseived 

 this method of reproduction in Suiirella splendida. 

 The union takes place at the narrow extremities 

 of the two frustules, the cellular contents mix and 

 soon there remains only an enormous sporange, 

 which the free valves of the two original frustules 

 enclose. 



The Rev. Wm. Smith has described something 

 analogous in Himantidium, but a careful exami- 

 nation of his plates shows that what he has seen 

 is in reality merely the rejuvenescence or return 

 to the maximum form without fecundation. 



3. In the third method the conjugation of 

 two frustules results in the production of two 

 sporanges, of two auxospores, and of 

 sporangial frustules (fig. 16). 

 This is the most frequent and best known method of reproduction 

 has been most carefully observed by a large number of diatomists : 

 Smith, Pfitzer, H. L. Smith, Ad. Schmidt and myself, &c. 



It has been observed in Epithemia, Cocconema, Gomphonema, 

 Encyonema, Colletonema, Navicula, &c. 



( ' ) Le Diatomiste (1894) ii., p. 95. 

 ( 2 ) Proceedings of Amer. Soc. of Microscopists, 1887. 



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